Counterstrike, Starcraft.

an essential need for online games: map maker.

wolfenstein enemy territory (pc) (its a free game from activision abundant with amazing mods)

-shooter that has literally thousands of maps. 

-character classes

-the ability to build and destroy bridges, gates, trains, whatever is needed by the mission

- one team defends and one attacks.  The winner being the team that completes their mission.

-haven't played in two years due to time constraints so i dont know how strong the community is now 

 warhawk (ps3) (it's epic) 

"Counterstrike"?

Are you referring to this?

R6: Rogue Spear and Day of Defeat!!

Ah! and ShockForce (aka Wulfram) <- I wonder if anyone here even heard of it?

F.E.A.R
Starcraft

Best in the future:
Starcraft 2, it will PWN all!

Battlefield 2 for PC

64 players online and i heard that the chinese even had a 128 man server!
Graphics where spot on in 2005 and still look ok now.
1 expansion pack and 2 booster pack
Ranking system and medals also.
A good balance of air, land and troop capability.
Many different classes and loads of unlockables.
32v32 players going against each other with tanks and planes is just the best!

Unreal Tournament 2004

Command & Conquer: Red Alert (put starcraft here if you prefer/i prefer RA)

Counter Strike 1.6

for massive shooter battles, the best i have ever played was Tribes 2, normally 32v32, but there were 64v64 servers. and they were real servers, not some legend from China.

oh and Tribes also gets an honorable mentions for JETPACKS!!

whoa 64 VERSUS 64???!! I can't even imagine what that would be like in certain other games..... I mean, Warhawk is pretty crazy with 16 vs. 16..