I just got one of these things weekend...works great, but might be uncomfortable for a passenger. Oh well... But for the lone commuter, this thing rocks. Its about $5 bucks at Wal-Mart and holds two drinks and some other stuff (cell phone - i-pod). I just have to put in some of that stuff you line shelves with.

http://www.saddlebags.com/Default.aspx?tabid=181