http://www.showerspass.com/

The Showers Pass jackets are excellent for this. I own the Double Century and the Elite 2.0 jackets. They are totally windproof (and rainproof, duh) but have exceptional ventilation designed into the jacket, including a huge opening in rear where the top half overlaps the bottom.

Great review of the Elite 2.0 here:
http://robonza.blogspot.com/2008/03/...0-cycling.html