Like carleton said, cycling specific jackets are cut longer in the back just for this purpose. My jacket is hiking specific, which worked pretty well too (for me, anyway), but cycling specific stuff is definitely what you're looking for.

There was a thread about this hoodie a little while back; lots of detail and comments about how much people loved it. Probably make for a good read (if you can find it), if you're interested in the hoodie.

My hiking jacket has a hood, which I had used in a really, really heavy downpour once. Most of the time, however, a cycling cap under the helmet should be more than enough.