I commute year-round, in the dark, in the rain, and have really liked Blackburn lights - really bright and they won't break the bank.

This year, I'm using the Blackburn Flea. ($36 CDN)

http://www.blackburndesign.com/Flea2_USB_front.html

I also have their Quadrant light.

I have had people stop me and tell me how visible and bright I am.