Everyone has given good tips. My biggest things are the rear fender (I have this one: http://www.performancebike.com/shop/...tegory_ID=6700

And shoe covers. I HATE wet feet. If you're riding in the rain to commute somewhere, I recommend bringing a change of socks for the ride back. Another trick I like is using ziploc bags to keep things dry. The sandwich size fit nicely in your back pocket.