Try reading this. It is a great intro to inertial sensing and some of the more popular chips. http://www.sparkfun.com/pages/accel_gyro_guide
As I said earlier if you want the platform to be inertially stable so that the pizza never has any net sideways force you could get away with a 3-axis accel. If you want it to be geographically stable (flat to the ground) you will need a 3-axis accel and gyro. I don't think this would be as good for a pizza, but it would be good if you had to stabilize a camera or a satellite dish. (More pressing problems) I don't see a magnetometer helping you in any way.
Hope it helps. Feel free to ask about any specific chips, but do a little looking first.