http://rakion.softnyx.net/

It can run kinda crappy, but its fun with a decent connection and will keep you occupied. 3 different game modes (capture the flag like golem wars, team deathmatch, and deathmatch) as well as a cooperative/exp gain mode (stages).

This is by the same company that makes gunbound if any of you play that...

Gunz online is a nice FPS / RPG also :)

i dont have a link right now, but ill see if i can find one sometime....