I've been thinking for a while now that it would be fun to make a monster that, like some of the traps in the DMG, could be partially disabled with a skill challenge. Truth be told, this sort of thing might be better as a custom-built feature for individual monsters, but I like the look of the templates in the DMG and wanted to try copying their techniques. My thinking is that, since a complexity 1 skill challenge is "equivalent to 1 monster", it would be appropriate to tack on to an Elite monster, since they effectively count as 2 monsters anyway.
I wanted to come up with a generic ability that would be useful for almost any type of big, tough monster with a weak spot, and the Juggernaut template below is my first crack at it.
Metroid Example
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DM: "The icy creature in front of you is armored in a thick, frosty shell that resists most of your attacks. You might be able to get it to expose the weaker, unarmored parts of its body, though... I'd say Athletics, Acrobatics, and Perception would be applicable."
Samus: "Can I start off with a Bluff check to trick it into charging past me instead?... 22."
DM: "Sure thing. That's a success. The beast rushes at you blindly, and I'll give you a +2 on your next check because it was a clever idea."
Samus: "Great! I'll try to use... hmm, Perception to identify the weak spot befre the creature can react. Oh, darn, that's only a 16 even with the +2..."
DM: "Failure. The creature twists toward you before you can get a clear line of sight, but you're pretty sure it's weaker in the back..."
Samus: "Oh, you mentioned Acrobatics, right? I'm actually pretty good at that one. I'll try to tuck and roll past it for the rest of my checks so I can get behind it. 23... 21... 27."
DM: "Nice! You tumble past the creature as it struggles to keep its eyes on you and deliver a quick blast to its back. The icy shell around it cracks and starts to melt - it's not going to have as easy of a time shrugging you off now!"
Juggernaut TemplateElite SoldierAny XP EliteDefenses +2 AC; +2 Fortitude
Resist 5 all at 1st level, 10 all at 11th level, 15 all at 21st level
Saving Throws +2
Action Point 1
Hit Points +8 per level + Constitution Score
POWERSHidden Vulnerability[INDENT]Choose a set of 2 or 3 skills appropriate for tackling or analyzing the juggernaut. For example, Arcana and Perception for a magically-shielded beast, or Athletics and Acrobatics for a massive, climbable creature. An adjacent opponent can engage in a skill challenge to discover or expose the juggernaut's weakness. DC 20 + 1/2 level, Complexity 1 (4 successes before 2 failures). Success negates all resistances the juggernaut has. Failure triggers the Knockback power (see below.)[/INDENT]
Knockback (immediate reaction; when an adjacent opponent fails the Hidden Vulnerability skill challenge; at-will.)
[INDENT]The monster makes a basic attack against the opponent who failed the skill challenge. On a hit, the target is pushed 2 squares.[/INDENT]
Resurgence (free; when first bloodied; encounter)
[INDENT]The monster regains its resistances if they were lost. Opponents may now attempt the Hidden Vulnerability skill challenge again.[/INDENT]
Sometimes breaking through defenses isn't quite appropriate, though; maybe you need to shut off an ability the monster keeps using with annoying regularity, like a breath weapon or a spell or even just a volley of arrows. For those cases, the Besieger template is more appropriate. For this one, the monster can't recover its lost power, but it takes a complexity 2 challenge instead of 1 to remove the ability.
Lord of the Rings Example
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DM: "The oliphaunt continues rampaging along as the archers seated atop it continue to make attacks. You can try to climb up and unseat them with Athletics or Acrobatics."
Legolas: "Excellent! I'll start with a couple of Athletics checks to scale the beast as it runs by. 26, and 32."
DM: "The first one fails, and you can't quite get a grip, but then your hands latch on to an arrow sticking out of the oliphaunt's side and you hoist yourself up."
Legolas: "Okay, some more Athletics, then. I climb the rest of the way up so I can cut the ropes holding the archery platform in place. 29, damn, 17, and 31."
DM: "You steady yourself atop the moving oliphaunt and move to cut the ropes as the archers panic. I'll need a couple of Acrobatics checks to make sure you don't fall off too early and can safely dismount."
Legolas: "Cool, cool, my Acrobatics isn't bad. 28, and... yes! 34!"
DM: "Great! You slice the rope holding the archers' platform in place and it slides off, and you do a quick tuck and roll to avoid breaking your neck on the way down like they did."
Besieger TemplateElite ArtilleryAny XP EliteDefenses +2 AC; +1 Fortitude, +2 Reflex
Saving Throws +2
Action Point 1
Hit Points +6 per level + Constitution Score
POWERSEndless Power (minor; recharge 4, 5, 6)
[INDENT]The besieger regains the use of an expended encounter power.[/INDENT]
Secret Weakness[INDENT]Choose a set of 2 or 3 skills appropriate for tackling or analyzing the besieger. For example, Religion and Insight for a ghostly mage, or Thievery and Acrobatics for a clockwork siege platform. An adjacent opponent can engage in a skill challenge to discover or expose the besieger's weakness. DC 20 + 1/2 level, Complexity 2 (6 successes before 3 failures). Success means that the besieger can no longer use the Endless Power ability. Failure triggers the Knockback power (see below.)[/INDENT]
Knockback (immediate reaction; when an adjacent opponent fails the Secret Weakness skill challenge; at-will.)
[INDENT]The monster makes a basic attack against the opponent who failed the skill challenge. On a hit, the target is pushed 2 squares.[/INDENT]
You could combine these two templates to create a solo monster, but it might be easier to just use a single solo template to make sure it all fits together. Like this Champion Guard template; succeeding on the skill challenge breaks down its resistances and negates its special attacks, but they'll come back for phase 2 of the fight once the monster is bloodied. DM's discretion as to whether or not the monster drops a Heart Container when defeated.

There aren't any Solo template examples in the DMG, so I just tried to approximate it. And to spice things up, I added a suggestion for creating a special vulnerability.
Legend of Zelda Example
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DM: "The giant beast swims past you in a lazy arc as it blasts you with jets of water. Its armored shell resists your attacks, but you can see it staring you down with a big yellow eye before each jet of water. You'll need to pass a skill challenge to crack this guy."
Link: "Let's go with Athletics, I want to swim in close to get a better shot at his eye. 25."
DM: "That's a success. You can see his massive, yellow, baleful eye glaring at you."
Link: "Hmm, I'll swim in even closer with more Athletics. 17, ooh! 29."
DM: "A failure and a success. You're close but can't quite reach the eye yet - you're fairly certain you're on the right track, though."
Link: "Is it close enough for me to use the Hookshot I found earlier against the eye?"
DM: "Yes. No check necessary, you line up a shot and the chain snakes out, latches onto the eye stalk, and pulls you up close. That's worth an automatic success."
Link: Okay, let me try Endurance to keep up my strength so I don't wear out. ... damn, only a 16.
DM: "Unfortunately, that fails. You can't quite keep up once the hookshot disconnects, and the beast shakes you free, dealing... 16 damage, and knocking you back to here. You can try again in a bit, though... but first, he gets to retaliate on his turn. Mwahaha."
Champion Guard TemplateSolo Soldier or ArtilleryAny XP SoloDefenses +2 AC; +1 Fortitude, +1 Reflex, +1 Will
Resist 5 all at 1st level, 10 all at 11th level, 15 all at 21st level
Saving Throws +5
Action Point 2
Hit Points +30 per level + (Constitution Score x 3)
POWERSEndless Power (minor; recharge 4, 5, 6)
[INDENT]The champion guard regains the use of an expended encounter power.[/INDENT]
Hidden Weakness[INDENT]Choose a set of skills appropriate for tackling or analyzing the champion guard. For example, Bluff and Acrobatics for a lumbering, dumb brute, or History and Nature for an ancient hulking forest creature. An adjacent opponent can engage in a skill challenge to discover or expose the champion guard's weakness. DC 20 + 1/2 level, Complexity 1 (4 successes before 2 failures). Success negates the champion guard's resistances, and also means that the champion guard cannot use the Endless Power ability. Failure triggers the Knockback power (see below.) At the DM's discretion, the monster may be vulnerable to a specific weapon or item; an opponent using this item automatically gains 1 success when attempting the skill challenge.[/INDENT]
Knockback (immediate reaction; when an adjacent opponent fails the Hidden Weakness skill challenge; at-will.)
[INDENT]The monster makes a basic attack against the opponent who failed the skill challenge. On a hit, the target is pushed 3 squares.[/INDENT]
Resurgence (free; when first bloodied; encounter)
[INDENT]The monster regains its resistances and the Endless Power ability (which immediately recharges) if they were lost. Opponents may now attempt the Hidden Weakness skill challenge again.[/INDENT]
Questions, comments, concerns? I'd love to hear what other people have to say about this. Yes, it's a little "video-gamey," as evidenced by two of my examples, but 4th Ed has proven to me that borrowing ideas from video games can be a really good idea if done well. Whether or not I've done it well... I'll leave that up to you folks to help me figure out.