Race of Champions (RoC)
Market Link: http://tinyurl.com/8856txc
This is a free but add-supported game. It offers two control types for the cars and runs pretty smooth on my Xoom. The gameplay is not really all that varied, so if you don't like racing circuit tracks, you'll get bored with this pretty quickly. It does offer racing ghost players who have raced which is very cool. So you get to race against a human, but just not in real-time.