Unless you can find a sever, multiplayer will probably only work for you in a LAN setting.

Games like prop hunt are great for some crazy fun...

Classic LAN RTS...

VS mode at a LAN party, although internet connection is required...

Smash, boom, crash... Car chaos... Chose demolition derby for crazy fun at LAN parties...

Eyeball bleeding fun, staple for any LAN party...

Epic, nuff said... Internet connection at LAN party required for this to work...

This only works in a LAN setting and has no real single player mode. This was taken off steam as online multiplayer was promised but never happened...

Nothing better then chucking toilets...

Can't go past good old CS...