+1The Blackburn Mars 4.0 is as bright as you get for that price, and very waterproof
http://www.tredz.co.uk/.Blackburn-Mars-4.0-Flasher-Rear-Light_22335.htm
HLaB said:+1
The Smart at least fails on when it gets wet (like palinrus says) but that only after a long soaking in a torrential downpour and there's no long term damage. I was a bit sick of that occasional failure however so I opted for the Mars 4.0 and I've been impressed with it.