Full fenders and a cycling-specific rain cape. You really stay very very dry (and well ventilated) in even heavy rain. ...unless it's raining sideways, in which case, play hooky.

I bought mine from Campmor a few years ago (link). Thumb loops in the front, thigh loops in the back to keep it in place; it's basically like a tent that sits over you while you ride. I love my rain cape.

The only part of you that gets a little wet in heavy rain with this setup is the lower half of your shins, in which case you can get some gaiters if you really really need'm. I've never bothered, though. No real need for rain pants with the fender/rain cape setup.

Carradice makes a high-end looking setup like this (link) that I haven't tried.