Game Server anyone ?

So I'm about to unleash a first person shooter game server from my fellow techies and readers. Its a massive, 6GB memory, Quad Xeon 3.2GHz monster with Raided drives hosted over a nice fat throughput. Now here's my predicament, I don't know what game to host ?

Any suggestions ?

I would like to have it up and running by the end of the month...so send it your suggestions ASAP. The majority wins.