Here is a game that I am keeping an eye on.
http://www.fortress-forever.com/?a=media
It is a mod for half-life 2. The idea is from a mod that was made by Valve for half-life called Team Fortress Classic. I used to play this game every day and I was very good at it. It is extremely competitive and it takes allot of effort to be good at it. This is the HL 2 version and it should be out soon. I have played allot of Unreal and Quake and I would say FF is the game you want to play if your looking for team competition.
It revolves around capturing the flag and there are 9 classes. You will either be playing defense or offense. You are bound to find at least 1 class that will keep your interest. The top clans will all be on voice comms, practice 2 or 3 days a week, and have well thought out strategies.