Hm... Well, Warcraft III, I have to admit was a great game. CS was nice too. I believe I have a few games I know of that I can throw at you. These are all the games that I have played that are f2p.
Maple Story (get's boring after a few months)
PangYa (Known as Albatross 18 in America. If you don't like golf, then it's not recommended)
FlyFF (I barely tried it, so I can't give any comments)
Rappelz (Haven't tried it. My computer can't handle it because I barely have any RAM. It looks neat though)
Ragnarok Online (private servers are f2p. Official ones aren't. The official ones aren't even as good though. My personal favorite is animaro.com)
Infantry Online (station.sony.com. Very fun shooting game. It's in a birds eye view format sort of.)
FantaTennis (Stands for Fantasy Tennis. It only has a Japanese release so far)
These are the games I can remember. I might have forgotten a few though. Try and find one out of this list that you might enjoy ^_^