I have this Cateye one, nice and bright and tough as old boots. The thing I really like though is that it can be mounted either horizontally or vertically when the clamp is on your seat post. I have it flat on the MTB and up/down on the road bike as othwise I'm aware of it.
http://www.chainreactioncycles.com/Mode ... elID=64502
http://www.chainreactioncycles.com/Mode ... elID=64502