Free Online First Person Shooters (Modern)

F.E.A.R. Combat

and if you have an nVidia card, you can get Half Life 2: Deathmatch for free here from Steam:

http://www.steampowered.com/nvidia/

both games are pretty fun.

and you are right, Warrock is kinda fun, but it needs help.

There is also numerous open source games available, Open Arena is one example, and if you have Half Life (the first or second) there are tons of free mods & total conversions to play.

America's Army and FEAR: Combat.

Combat Arms is new and its similar to WarRock and Call of Duty, but alot better then WarRock.

Combatarms.nexon.net