Active:
Spectromancer (online strategy card game) - my primary game at that moment
CS: Source (FPS) - some shooting for fun 
World of Warcraft (arena PvP / MMORPG) - soon i will start to play it once again with friends
Recent games:
Massive Assault Network 2 (TBS/Wargame) - classical wargame online. A little too slow for my style, but a really good game with a good multiplayer balance, ladder and tournaments.
Quake Live (FPS) - repackaged Quake 3 is nice indeed, but where are Russian servers? It's kinda hard too shoot with a railgun with a 65+ ping, i still hit 50%+ of the time but it's kinda sad anyway.
Future games:
Starcraft 2 (RTS) - i played Starcraft, soon it will be time to "return and experience the adventure once again" (c) Blizzard, Warcraft 3 promotion video. The best competitive RTS, first professional cybersport game, now with the better interface and a better online lobby / ladder. Count me in 
Since I prefer to play with people I can chat to afterwards and keep contact with on forums or IM I tend to not play MP so much....got this resistance to MP since people online do everything to win and I get put off by that feeling....
You're supposed to do everything tournament-legal if you want to win 