I have a couple of pairs of Columbia rain pants. The better ones have a mesh inner liner, and a waterproof durable outer shell. I wear them over cycling tights or shorts. No problems with sweating or freezing when it's ~60 - 30°F. My commute is 6+ flat miles, in 30 - 40 minutes.

I also have inexpensive PVC rain gear, similar to that recommended by [MENTION=197614]fietsbob[/MENTION]. I'm more prone to sweat in that, but it keeps me dry even in heavy rain.

Best prices for Columbia and similar are the clearance sales for department stores and big box sporting goods stores, e.g. Kohl's and Dick's online.