This weekend only, pick up Codemaster's Race Driver: GRID for 50% off.
For $30, I'm not too sure if it's worth grabbing GRID on the PC. For $15, however, that's an entirely different story. It might soon be outdated with DIRT 2 on the horizon, but for half price that isn't too much of an issue. It's still a fairly new game, with shiny graphics and a realistic driving engine. I mean, it's not like there are too many racing titles on the PC anyway. I doubt you're going to pop in Auto Assault anytime soon.