NOTES:
I envisioned two principal themes while exploring Zendikar's Merfolk [cards]: exploration/scouting and knowledge.
They are described as solitary in the sense that they enjoy researching in solitude, but most of their abilities benefit their allies as a group. They have a leader streak mechanically, without actually being charismatic. They lead with their knowledge.
There were many powers that fitted as a racial power for them, so I decided to make a single power with many uses depending on the merfolk's power source. This encourages hybrids and/or multiclassing, and makes the Bard an attractive class for the merfolk (which is thematically fitting IMO), even if Charisma is not given a bonus.
Their other signature ability is knowing an extra encounter or at-will power of their level but needing to swap it with another one in order to use it. It's like they all have a mini spellbook, which I think is fitting because they're listed as wizards more often than any other class, and this power swapping during resting also sounds as something a solitary explorer/researcher could do, to prepare him or herself to the next challenge in advance.
The explorer feature can be powerful and it can be extended to allies via feat: extra move action during surprise rounds. Note that it can be combined with the racial power, which is a minor action, and can thus be used by burning a move action if need arises.
Last thing, maybe the most overpowered, the racial power doesn't scale with level in quantity of bonus, instead gaining more uses per encouneter. Two at paragon and three at Epic. I thought that maintaining the effects low, it could have been a good way to represent the resourcefulness of the Merfolk.

PEACH!!

MERFOLK

"Curious, thoughtful, and analytical, the merfolk are natural  explorers. Although the merfolk are born in the water, their appearance  is more human than fish. They have muted skin colors, including ivory,  beige, silver, and pale gold. They have residual fins on the backs of  their arms and calves. The fins are sometimes streaked with brighter  colors, such as green and blue. They have human-like hair in shades of  silver, gold, and light browns. But like their fins, the merfolk's hair  often has streaks of bright color as well."

Racial traits

Average Height: 170-185 cm
Average Weight: 45-70 Kg

Ability Scores: +2 Int; +2 Dex or +2 Wis
Size: Medium
Speed: 6 squares, Swim 8 squares
Vision: Low-Light

Languages: Common (?) - Choice of two other
Skill bonuses: +2 Arcana, +2 Religion, +2 to any other skill of choice

Aquatic: You can breathe under water and you have a +1 bonus to attack rolls against creatures without the Aquatic keyword inside water.
Solitary Training: Choose an at-will or encounter power of your class that you could have had at your level. During a short rest, you can swap one of your at-will or encounter powers of the same type and level with the one you chose. You can retrain this power normally.
Twitch: When you're granted an Opportunity Attack you  can instead shift a number of squares equal to the highest of your  Dexterity, Intelligence or Wisdom modifier.
Uncanny Scout: During Surprise Rounds in which you can act, you can take an extra move action.

Deep Roil Sense - Merfolk Racial Power

Your keen mind makes you sense the Roil of Zendikar in a way unique to your race, allowing you to morph your powers around it, to the advantage of both you and your allies.

Encounter Minor Action      

Effect: Choose one among those that match your power source(s)
     Arcane or Psionic: Until the end of your next turn, you or one ally in sight can slide each creature you or he/she hit a number of squares equal to your Int, Wis, or Cha modifier, whichever is higher.
    Divine or Primal: Until the start of your next turn, both you and an ally in sight gain a fly speed equal to your land speed.
    Martial: Until the end of your next turn, both you and an ally who can see you do not provoke Opportunity Attacks and gain a +2 bonus to speed.
    Shadow: Until the end of your next turn, you or one ally in sight have Total Concealment.

Level 11: You can use this power two times per encounter.
Level 21: You can use this power three times per encounter.

FEATS

LEADING WITH KNOWLEDGE

Knowledgeable Mentor
You are remarkably good at teaching your companion your tricks, providing you share a knowledge base.
Prerequisite: Merfolk
Benefit: During a short rest, one ally can swap one of his or her powers with your Solitary Training power, as if he or she had the same feature, providing the power matches his or her class's power source.

Scouting Team
You can coordinate with an ally so that you can both advance at your uncanny pace.
Prerequisite: Merfolk
Benefit: During a surprise round in which you can act, both you and an ally within 5 squares can take an extra move action.

Divert The Flow
Your superior insight and reaction speed is enough to make an ally exploit an opportunity in the way you suggest with your actions, altering the flow of the battle.
Prerequisite: Merfolk
Benefit: When you shift thanks to your Twitch racial feature, if you end up adjacent to an ally you can use Aid Another as a free action. The ally can then shift the same number of squares as an Immediate Reaction.


NEW NOTES:
I had to remake the thread due to strange bugs of the forums, and took the Opportunity *chuckles* to give the Merfolk the Opportunity Aid feature. As you can see, it's situational and not game breaking. Becomes more powerful after taking the Concerted Opportunity feat, so please evaluate it carefully and mercilessly critque!
I would also like to know if you see it appropriate for Merfolk and if you can find a better name, more flavorful or Merfolk related!
I also changed the name and fluff of the racial power thanks to Gamma-Mage suggestion: the new fluff fitted seamlessly!!

LAST CHANGES:
Thanks to Gamma-Mage suggestions, the new racial feature now has a better and even Zendikar and Merfolk related name. But I toned it down a bit, adding to it with the related feat.

Nov 12, 2010 -- 5:36AM, Gamma-Mage wrote:

Nov 12, 2010 -- 2:21AM, LordArchaon wrote:

if you can find a better name, more flavorful or Merfolk related!

Is Twitch too simple for a skill name? There's also Unified Will , which sounds good, and has lullmage flavour text.

Wow, that's the kind of advice I asked for! Unified Will is a perfect name for the "Concerted Opportunity" feat, while Twitch could be good but too cryptic... "Opportunity Twitch", could be the best guess for the feature! Speaking of Lullmages, I could also envision a truly "lullmagic" feature in place of this aid-another-thing. However, Unified Will also suggests that it's a Merfolk thing that of preferring to help others against their enemies instead of fighting directly. What do you think Gammage?

Updated and changed! Twitch it is, and simplified because it was a bit too much... (Yes, Merfolk are my favorite on Zendikar...)

Reduced the flying duration of the racial power after the playtest revealed it was too powerful.