Frogg Toggs are excellent. I've used a set on several long-distance trips in the last few years and have been quite satisfied. Stayed completely dry. Added benefit is that they breathe, so you don't get steamy if you're riding in warm, wet weather.
I also have the expensive Aerostitch gear, which works well, but I say save your money. Buy the Frogg Toggs and wear your regular gear underneath.