http://www.joinfear.com/main

Its the multiplayer portion of F.E.A.R., free to download and play. They give you a CD-Key for online play and everything.

Haven't done it yet, as I'm at work. If you're getting slow download speeds, you can try this torrent:

http://torrents.vugames.com/fearcombat_en_107.exe.torrent (http://torrents.vugames.com/fearcombat_en_107.exe.torrent)

(Which I also have not tested)