The most important raingear is fenders. I don't mind getting rain on me, but I don't want to get muddy.
After that, a helmet cover and a breathable (vented, not fancy-pants fabric) jacket; mine is from J&G at bicycleclothing.com and works great even in downpours.
I just let my legs get wet unless it's < 40*F or so, in which case I put on some tights and cheap nylon shell pants so at least I have warm water and not much wind on my legs.