IME, caps may help in a light rain but when the rain gets heavier, the glasses just have to come off. I think cycling caps are kind of retro cool but I rarely wear one for a couple of reasons. They are hot compared to a headsweats beanie. Also, looking out from under the brim requires that I hold my head up at an uncomfortable angle. What I like is that they fold flat and easily fit in a jersey pocket. I always carry one if I plan to stop for lunch in the middle of a ride. Nashbar often has retro team caps cheap.