Did you consider using a MicroGyro? (
datasheet) These are the same type of gyros as used in the Wiimote, and in the Gyration line of human interface devices for computers (
wireless 'flying' mice).
They proveide a ton of accuracy, however I dont know how well they'll do in the harsh environment of a FIRST field... think the vibration might kill it, but who knows. I havent found a source for these yet but I'll look....
-q