I knew I missed a bunch game types that would occur to me after.
Percentile (Warhammer)
Unisystem
Gurps
I mostly play pathfinder lately. It's the most commonly run game in my gaming group, though when I run it it tends to be heavily houseruled and be more of a merger of Trailblazer and Pathfinder, with extra houserules I added myself.
None of us play AD&D or OD&D and their derivatives, but we have some WoD, Warhammer, and Savage Worlds floating around.
Our gaming group is big (university RPG club, 30-50 people in various games) and we have one 4e player, and only one guy who will GM it, though he'll only do it to boost advertising at our monthly mini-conventions.
My ideal system doesn't exist yet, and I've been slowly putting it together. 3.5 Derivatives come in second.