I've found that for light to moderate rain a jacket like those already described (gore-tex or equivalent, pit zips, extended back flap) works well and cycling pants with gore-tex type front panels and breathable, stretchy type back panels (available at MEC - Mountain Equipment Co-op:
http://www.mec.ca/) work very well.
In heavy rain I dress for warmth because your going to get wet, either from within or from without.
Bubba