Online Multiplayer Games (PC Platform) with a big user base/community still

I've been getting the itch to play some online multiplayer on my PC. I was wondering if anybody knew of some titles (any genre) that have big communities and a lot of online-gamers still.

Here are games I know that you can still find a lot of online-multiplayer users:

1. Starcraft Broodwar (and any Blizzard released game after that).

2. Team Fortress 2

3. Company of Heroes (RTS)