I used a pair of Firstgear Rubber Rain Boots this season for riding in the rain. The pros are they are light, pack really small and are waterproof. The cons are they are easy to poke holes in and tear. For 15 bucks they are okay - but I'd like something I don't have to replace too often.
I ordered a pair of NEOS Adventurer™ overshoes that cost a bit more (4X) but I think they will do the job and last. The reviews from motorcycle riders on the Aerostich website are positive. They have a nice grippy looking sole, weigh a couple of pounds and pack down to a size of tennis shoes. I'm hoping I don't have too much opportunity to use them until next Fall - but the way this summer is going it's hard to say. I'm sure they will come in handy for commuting and on some road trips.
I like the idea of being able to wear comfortable leather boots and put on waterproof overshoes when I need to, rather than trying to find a waterproof all-around type boot. I'm afraid those would either not breathe and be uncomfortable and too hot - or breathe and not be waterproof. They might be some fairly expensive gore-tex boots that work...but I've already got a pair of leather boots I like, so I'm going to try overshoes for awhile.
NEOS is an acronym for New England Overshoe Company.