I've got the Cateye Velo 8 ($30). It counts calories but I had to have that feature to get the avg MPH feature, which I wanted. You can get the Velo 5 for about $5 less sans calorie counter or avg spd.

I don't know about the aesthetics of them...they're not very noticeable. I don't know of any computer that can easily be switched between bikes, however, there is probably one out there.