Warlords (especially the Tactical variant) are notorious for granting their allies free attacks by the bucketful.
The effectiveness of this approach is very much dependent on party composition.
While it's nice to imagine a perfect Warlord party with awesome basic attacks, in real play the composition of your party is usually out of your hand. Forcing your party members to play certain classes and builds just to take advantage of the free attacks ... that's likely to get you uninvited from the campaign.
But there are low-cost methods to optimize your current party for free attacks, methods that you can subtly (or not so subtly) suggest to your party members.
I'm proposing three categories of free attack optimization:
Optimize power MBAs (melee basic attacks) are the most commonly granted free attack. Most melee classes have decent MBAs out of the box, but there's still room for improvement. RBA (ranged basic attacks) are not as commonly granted as melee ones, but they are often the only choice for many classes and builds. As a Warlord gains levels, his/her powers (e.g. Hail of Steel) starts granting basic attacks, which allows non-melee classes to join in the fun. This category refers to how to improve the ally's MBAs and/or RBAs. Specifically, improving the attack bonus, improving the damage, and improve the rider/add-on effects.
Melee Training (heroic feat) allows you to use a non-Str stat for MBAs. This is especially useful for classes with non-Str primary stat (e.g. Wizard).
Magic weapons with always-active, on-hit properties. E.g. Challenge-Seeking weapon. This improves your free attacks as the weapons's properties do not require activation. Free daily action weapons are another option, although not as optimal.
Weapons with high base damage. E.g. Brutal weapons, high-die weapons. This one is obvious, but sometimes your ally needs a bit of a nudge.
Weapons with high proficiency. Again, obvious, see previous method. A subclause: wield weapons that you are already proficient with, even if they have lower damage.
Class powers that counts as MBAs. Since powers are almost always better than a basic attack, this one is a no-brainer. See the class-specific list for more details.
Weapons with heavy-thrown property is great for melee allies, as they use Str. Such weapons are often passable melee weapons as well. Magic weapons are even better as they automatically return whent hrown. Note that Melee Training cannot be used for ranged attacks, so non-Str allies will have to consider light-thrown weapons or other options.
Optimize reach and response No matter how optimized your basic attacks are, they are entirely wasted if they cannot reach and hit the enemy. Hail of Steel, for example, allows the party to make basic attacks against a target. If you're a guardian fighter and you're not next to the target, you can't attack, because the power does not grant you movement. If you're a crossbow user and it's not loaded, you can't attack. The Warlord may have powers to move allies into position prior to granting attacks, but that's not always the case. Triggered powers are especially cruel in this regard because they are more difficult to predict and setup. This category deals with improving the party's reach and response, so that they can actually utilise the free attacks when they are granted.
Speed Loader (heroic feat) allows you to prep 'load minor' crossbows as a free action, allowing you to make RBAs with with such crossbows.
Quick Draw (heroic feat) allows you to draw a weapon as part of the attack. Allies who don't usually wield thrown weapons can use this to draw a backup thrown and make a RBA. Caveat: if you don't have a free hand, you'll have to drop your current weapon since sheathing a weapon is a minor action.
Reach weapons (e.g polearms, spears) means that you don't have to be adjacent to make a MBA.
Weapons with heavy-thrown property has been mentioned before, but is worth repeating as this is probably the least disruptive method for melee allies to utilise free basic attacks. Sure, it won't be as lethal as their melee attacks, but it's better than nothing in scenarios where they cannot be in position to unleash melee attacks.
Optimize charge Quite a number of Warlord attacks grant free charges. Iron Dragon Charge comes to mind. Most classes have some charge options, although a few like Druid and Barbarians stand out as abundantly blessed in that department. Charges are unique in that they combine power and reach in the same package, and relatively easy to optimize.
It's hard to go past the cheap Badge of the Berserker, which allows to you charge without provoking OAs. Charge-happy builds will probably have this anyway.
Class/build specific methods
(Special thanks to Mengu74 for a massive list of methods)
Power of Skill (as with all Divine Classes) is great here - turns Overwhelming Strike into MBA. [Ignis_Fatuus and Mengu74]
Great out-of-the-box support from crit effects and censure effects [Ignis_Fatuus]
Consider focusing on charge-happy attacks.
Strength Cleric - They already have good basic attacks, but Power of Skill can help improve even that with a basic attack Righteous Brand. If your DM allows it, go first with your basic attack so that all subsequent party members gets the Righteous Brand attack buff. Nasty. [Mengu74]
Savage Rend can be used as RBA.
Totems are one-handed, so wielding an off-hand thrown weapon gives you reach and response, although probably not much power. Quick Stow is then required to keep the weapon between shape shifts, alternatively Quick Draw can be used to draw and attack.
Tempest Technique allows you to wield an off-hand thrown weapon and still have good defenses, which means you can respond to free attacks even if you're not adjacent.
Bonus: Fighter will automatically mark the target with the free attack. [Mengu74]
Wicked Strike (Dragon Mag) is good for a 2-handed fighter. [Mengu74]
Several nice charge options, e.g. Knockdown Assault and Hunting Wolf Style. [Mengu74]
Avenging Light can be used as RBA.
Sun Strike can be used as RBA.
Divine Bolts can be used as RBA with Power of Skill. [Mengu74]
Virtuous Strike can be used as MBA.
Power of Skillallows Valiant Strike to be used as basic attack. [Mengu74]
Ardent Strike is a good charge option for Cha-based Paladins. [Mengu74]
Dagger should be the weapon of choice (and usually is). If they're magical, then the Rogue is fully covered in terms of power, reach, and response.
Adaptable Flanker makes it easier for you to apply Sneak Attack damage (if you haven't already in this round).
Dragonfrost can be used as RBA.
Acid Orb can be used as RBA.
Sorcerous Blade Channeling may be able to convert RBAs to MBAs, which means that your Sorcerer can join in the free melee attackfun. I said 'may' because the rules seem quite open to interpretation and controversy, so check with your DM first. [Merlin the Tuna]
Eladrin + Fey Charge + Eladrin Swordmage Advance = Teleporting double attack when granted a charge. Scary. [Mengu74]
Some Guardian Forms give you fantastic basic attack support [thanks to Mengu74 for pointing this out]. Here's a quick list:
Fearsome Ram - push 1 on hit
Oak Sentinel - reach +1
Rowan Sentinel - reach +1
Sand Sentinel - ally gets THP on hit
Autumn Reaper - extra damage
Blood Wolf - prone on CA hit
Jungle Lord - slide 2 on hit
Chimera - push or prone on charge hit
Eldritch Strike can be used as MBA.
Eldritch Blast can be used as RBA.
Pact weapons improve the power of your basic attacks.
Inevitable Wave is a hilariously effective charge option if you happen to have two Warlords in the party. [Mengu74]
Magic Missile can be used as RBA.
Notable Magic items
Eagle Eye Goggles - +1 bonus to RBAs.
Rapidstrike Bracers - Once per encounter turns your basic attack to any of your level 1 at-will attacks. Fantastic, but the arm slot is very competitive.
Badge of the Berserker - Charge without provoking OAs.
While this thread is focused on helping any class and build to better take advantage of Warlord's free attacks, it's worth mentioning that some classes and builds don't need that help. If you happen to have these Warlord Buddies in your party ... lucky you (and lucky them). So, if your group actually volunteers to fully optimize themselves to take advantage of your free attacks, you know which classes to start with. Or, if you are invited into a party that just happens to have a high concentration of Warlord Buddies, that may just sway you into choosing to play a Warlord.
Most Avenger builds, especially with MBAs. They are accurate (oath of enmity), have access to good on-crit effects, and can benefit from censure effects. They also have good access to feats and powers that power up their MBAs. Note: Melee Training, or better yet, Power of Skill, is compulsory.
Strength-based Rogues, especially the dagger-using variety. Solid MBAs and RBAs, and because dagger is both melee and ranged, they have reach and response covered by default. Free attacks also allows them to retry Sneak Attack if their normal attack for the round missed.
Rangers. The archer builds have great RBAs with great power and range, allowing them to really utilize any free basic attacks. Can't really utilize MBAs, though. The 2-weapon builds naturally tends toward MBA-enhancing options to maximize mileage out their multiple attacks, and therefore a default good choice for free attacks. Just like Rogue, free attacks allow Rangers to retry Hunter's Quarry damage if their normal attack for the round missed.
Barbarians, especially the 2-handed weapon variety. Big damage on MBAs and loads of charge options. Nothing more need to be said.
Fighter, especially the 2-handed weapon variety. Big, accurate damage on MBAs. They are usually next to enemies, which gives them reach. The free attacks lets them mark more enemies, which is always a bonus. Some feats like Pinning Challenge is icing on the cake.
A couple of magic items strengthen basic attacks, most notably Eagle Eye Goggles. Other items include Bracers of Mighty Striking/Perfect Shot and Rapidstrike Bracers, although the arm slot is usually occupied by other items.
Actually the warlord, from paragorn and up, can both grant ranged basic attacks or generic basic attacks (mean melee or ranged) whit ease, it's just matter of power choice. Just look at Warlord Indignation (encounter) or, to point an high level daily, Relentless Assault. And there are lot more, ever at lower level.
Nothing. My old party is full of short-sighted racists and sexists (on their own admission), so I left.
Warlords have almost nothing that can grant an ally a ranged basic attack, so there is not much advantage a warlord can grant to a wizard or warlock on that front.
Brash Assault, Concentrated Attack, Lead by Example, Provoke Overextension, Surprise Attack, Stay on Target, Unified in Blood, Ventured Gains, and Beat them into the Ground all ganged up on you with ranged basic attacks. They didn't even bother inviting their level 15+ companions to the party.
Avengers are great for granting basic attacks too as they really profit from the extra chance to get a crit and if the granted attack is timed so as to coincide with the censure bonus being just triggered, all thye better.
Avengers don't have a power that can be used as an MBA, but almost all will take melee training anyway. Followers of certain gods gain access to the feat Power of Skill which makes Overwhelming Strike into an MBA, now they can shift and slide on the attack you granted!
I think there is something every class can do to help gain some benefit from a warlord granted attack. Strength primary or secondary classes already have it easy. I've seen a dragon sorcerer stab someone in the eye with a dagger for the kill. If strength is not your primary or secondary stat, it can start to get a bit tricky but counts as basic attack is available to a lot of such classes. Here is a quick look (skipping some leader classes since it's not likely to see them side by side).
Strength Cleric - they already have good basic attacks, but power of skill can help improve even that with a basic attack Righteous Brand.
Wisdom Cleric - unless you're on odd elf build with high dex who can do decent basic ranged attacks, not much the cleric can do, other than get melee training, but even that is probably not worth it since your laser cleric should be safely in the back for the most part.
Fighter - fighters mark with basic attacks. What more do they need? Wicked Strike could be interesting for extra damage. And Knockdown Assault and Hunting Wolf Style Crushing Surge are good for the charge happy warlord. And battleragers will have an easier time getting temp hit points, or their bonus damage with a warlord around to grant them extra attacks.
Strength Paladin - Power of Skill again is not bad for a basic Valiant Strike.
Charisma Paladin - Virtuous Strike is obviously good. But Ardent Strike can be a better choice, if you have a warlord who likes to grant charges instead of basic attacks.
Ranger - Out of the box, these guys are already optimized for basic melee or ranged attacks. For versatility, quickdraw may be a good option.
Strength Rogue - not much to do.
Charisma Rogue - I think it's worthwhile for a charisma rogue to get melee training dex, if they have a warlord in the party.
Warlock - Eldritch Blast or Eldritch Strike takes care of the basic attack part.
Warlord - Two warlords in the same party is pretty unlikely, but they can get some interesting synergy going with on focusing on charge granting powers, and the other with Inevitable Wave.
Wizard - Other than Magic Missile, not much going on there, though I have seen one wizard who liked to whack people on the head with his staff.
Avenger - Power of Skill or melee training is nearly mandatory for the avenger any way. As for basic ranged attack, they just got one of those too.
Barbarian - they like to charge, so the warlord should look for powers that give them charges. But their basic attacks are quite brutal out of the box as well. And when they kill/bloody targets, they can do free action stuff to boot, not to mention when they crit. They don't really need any extra attention or help.
Druid - if there is a warlord in the party, the druid should definitely grab Savage Rend (or Grasping Claws if you must), and/or possibly Pounce. These are good powers any way, so no reason to ponder. If I were a druid with a warlord in the party, I'd also look at grabbing a summon power. When all alies get free basica attacks, the summoned critter can join the party too.
Invoker - Avenging Light is good. Divine bolts with power of skill would have been good, if Hand of Radiance hadn't trumped it. Forget basic melee.
Sorcerer - Already mentioned dagger in the eye. Strength Sorcerers are already good in basic melee, but could consider Acid Orb or Dragonfrost. Dex Sorcerers can throw their dagger if they have to.
Warden - strength primary means they are doing fine. If they are in a guardian form, they sometimes do fun stuff with their attacks, so there is again enough synergy there. Warden's Lunge might be worth a look with a charge granting warlord.
Assassin - They already have good basic ranged attacks, so quickdraw might be handy. And they need melee training if they want to be able to charge anyway, so they're set.
Swordmage - the Assault swordmages are already set. Others need a form of melee training anyway. And, Fey Charge + Eladrin Swordmage Advance. Enough said.
tiornys - Thank you for the tip, I'll start a Magic Item section.
Ignis - I'll add that to the Avenger section.
Mengu74 - Wow, fantastic list. I'll add them next time I have the chance to sit down and edit. Power of Skill blew me away, I never knew that feat existed. A definite must for divine classes wanting to optimize their basic attacks. Righteous Brand as a basic attack? Nasty. And great call on summoned critters. Again, fantastic list.