You must check out Nexuiz and Warsow as they are just AWESOME!!

Oh, and i've just discovered an excellent driving game similar to Grand Turismo. The graphics are really good and the driving is pretty realistic. Not that i've ever driven a car......

Racer
Game Type: Racing
License: Free/Open Source

Racer is a free cross-platform car simulation project (for non-commercial use), using professional car physics to achieve a realistic feeling and an excellent render engine for graphical realism. Cars, tracks and such can be created relatively easy (compared to other, more closed, driving simulations). The 3D, physics and other file formats are documented. Editors and support programs are also available to get a very customizable and expandable simulator. OpenGL is used for rendering.

Racer only comes with one car and one track. However, lot's more are available here