I'm currently playing in HarnWorld. Harn is a little known rules independent setting known for its detail and realism. There are several thousand pages of free fan produced Harn articles on www.lythia.com and it is easy to drop many of these into exsisting or home brewed settings.
Currently I'm running Monte Cook's WoD, which we'll be breaking on in November.
Next I plan on giving Mongoose's Runequest a spin using either Lankhmar, Hawkmoon or the Elric setting. I really like what I've seen so far and enjoy the whole real swords and sorcery vibe. The different magic systems have also given me plenty of ideas for homebrewing as well. Lastly I like the fact that Mongoose distributes their gaming magazine(Signs & Portents) in free full-color PDF format.
Recently I've played
Qin:The Warring States
Star Wars saga ed.
3 D&D 3.5 PBEMs
1 1:1 Mutants & Masterminds PBEM, set in a modern-ish reinterpretation of the Marvel Universe of about 1983.
May soon be playing:
a 1:1 Alternity game
Desperately want to play, but have never found a good group interested:
Exalted (I like crazy anime action!)
Vampire (Bought some Masquerade stuff years ago when asked to run a game of it, then that fell through. Still greatly enjoy most of the setting.)