I've been using Nashbar's waterproof rear panniers for the last couple years both for touring and for utility shopping trips. They have a little less capacity: about 40 l, but leave the top of the rack free so you can easily load some items (typ. tent, sl. bag, sl. pad) up there if needed. I can fit all of my touring load inside the panniers and a small handlebar bag. Nashbar runs lots of sales so their price varies considerably. These panniers usually sell in the $30 - $50 range when on sale. So far they seem to be holding up fine. They're pretty basic with just a single large compartment and just clip closures (no zippers).