I just got a pair of large Avenir excursion panniers. I probably only have about 150 miles of commuting on them, but I like them very much, considering the price. Easy to get on and off. Generous outside pockets. Attachments for additional straps.

They're not waterproof, but my experience is that if I don't want it to get wet, I put it in a plastic bag. I've had many things, shoes, jackets, even a boat, that were supposed to be "waterproof" but turned out not to be.