My favorite is Plants vs Zombies. The plants in the game are so cute that I love them very much. I play the game again and again, but still find it very funny.
Definitely World Of Warcraft, especially when 25man (including me) can kill Arthas (World Of Warcraft highest boss at World Of Warcraft III -Lichking)
my favorite game is Bloody roar, 2 player is battle. but I don't know where I can find this game?? because I just have this game on version Play stations (PS1 and PS2)
I'm a Counter-Strike fan so its my no1 game however I found a great online flash game called "Hot Dog Bush", very addictive tiny game
My favorite online game would be Cabal Online for F2P games and Guild Wars when it comes to P2P games.