I think fancy rain gear is a waste of money. Like supcom said, you have a choice between warm/wet (from sweating) or cold/wet (from rain).

In warm rain, I just wear my normal clothes -- bike shorts, gym shorts over that, and a wicking t-shirt (nothing cotton).
For cold rain, I wear a base layer, wool sweater (it's actually 50% cotton but that doesn't seem to be a problem), and fleece tights. I get wet but stay warm. If the rain is very heavy, I might wear a cheap plastic rain jacket -- which keeps the rain off but causes me to sweat like crazy.

The rain jacket cost maybe $30, everything else I already had for dry-weather riding.