There are all kinds of waterproof "breathable" fabrics and products out there. I've tried several and they are waterproof but only "breathable" to a point. I haven't found a jacket yet that is well ventilated enough to keep me from sweating if I'm riding at a good pace. It gets worse with the more layers you might need to stay warm (for instance this week when I commuted in the mornings with temps that were 15-20 degrees... and still arrived at work sweating.)

For moderate temps 45-65, I've heard good things about the showerspass jackets... and someday I'll give them a try.