If you are looking for some motorbike racing, MotoGP ’06 is now on the Xbox Live Marketplace unders “New Demos and Tailers”. The download weighs in at 882.53MB, but it looks like it has a fair bit of content.
You can play on Xbox Live, or single player. You can race 2 classes in single player, Extreme 1000 and Grand Prix, both containing one track, and one rider in each class, and you get the same to use online against your friends.
Good luck with downloading it, as more people grabbing it have slowed it down to a crawl for me.