[url=http://www.splashdamage.com/content/wolfenstein-enemy-territory-barracks: Enemy Territory]Wolfenstein: Enemy Territory[/url]
You can't possibly go wrong with what has to be one of the best team-based shooters ever. I don't know how many people you are, though. You need at least four people for it to make any sense, with six it's already highly playable IMO.
Edit:Ah crap, sorry. I read "my friends". Didn't notice that it's just two guys. Well then ET doesn't make much sense...
Fear Combat It's a standalone version of the multiplayer component of F.E.A.R.. I haven't ever tried it but I know some people who enjoyed the hell out of it.