Quake Live
Quake Live is an arena style FPS making it's tournament début July 31st - August 3rd 2009. The game will be completely free. Although designed primarily for online competitive play an offline bot mode will be available. Quake live will be played using a browser and is developed by id software.
It's really cool that Quake live is being released entirely for free, it will be good to see an arena game widely used for competitive play, as the arena genre is quite dead at the moment.