I've found that Gortex is a must. It blocks the wind, stops the rain and is easily packable. In summer on long rides, when you hit a thunderstorm and it's hot, the Gortex breathes to let the heat out so you don't sweat your a__ off.
Go to Cabellas online and take you're pick. I always buy North Face because of the quality. It will last for years and not end up looking like a torn rag after 100 miles. Make sure there is a series of snaps or velcro on the pants by the leg openings. This way you don't need to take your boots off when you put the pants on.
I rode to the 95th in Milwaukee from Calif. 5 days of solid rain and it rained while we were there. Also wore Gortex boots. Dry as the desert the entire time.
Best
dave29