I've been using one of these for autocross...pretty neat.

http://www.race-technology.com/dl1_8_936.html

The software is more road-racing oriented than autox, so it's a little awkward to do the analysis, but interesting. I'm only using the accelerometer and GPS data at this point, but the thing will handle a ton of other inputs...would be cool to add stuff like throttle position, yaw sensor, wheel speed sensors, etc.