I've been using the Ultrafire WF-501B from DX about a year now. I also bought 3 of them for my friends, one of whom commutes to work everyday in any weather conditions, including rain. I twice rode under torrential rain with two of these on. These flashlights are awesome, very bright, so bright in fact, that I stick a Kinder Surprise plastic shell on it at night! The shell from the egg fits well, really tight.

I'll upload some photos later. I use the universal bike mount, zip-tied to the rear rack.