I am a little disappointed no one took one in my current campaign but the leader type class that was taken is a Bard, and I have been very impressed. His powers just reinforce the idea that hit points are about a lot more than physical damage capacity. That has always been the case, but 4th takes the idea and runs off with it like no other edition has. "Vicious Mockery" is a ranged, damage-casing attack for a bard and it is hilarious to see it in action with a good group. More about bards in another post.
The other leader types in the game are Clerics and Shamans and they do their thing just fine, but "Leader" has mostly been translated as "Healer" and with the Warlord (and the Bard too to a degree) this is just not the case. It's more like "Catalyst" as they make the whole party better, period, and are not just reactive defensive save-types like Clerics often have been - healing, curing, dispelling, etc.
Anyway, if you don't play 4th but have a chance to look at a 4th ed PHB take a look at the Warlord and see if there aren't some ideas there worth adapting to your game. Maybe it's a variant of Paladin - instead of bonuses to saves for himself maybe he grants a bonus to hit for allies within 10'. Maybe his holy avenger grants a healing aura instead of a dispel magic aura. I've had a few thoughts in this direction myself but I have yet to do anything concrete with it. We'll see what happens when my basic game gets rolling again next month.