I like the Detours bags. This is the one I have:
http://detours.us/catalog/product_in...2eb01ebfb8563e
mounted on a Blackburn rack. Or if you like the seatpost mounts, maybe:
http://www.rei.com/product/724934 (they also have an expanded version of this one)

These are really nice bags, water-resistant with a hi-vis yellow waterproof cover if it really rains hard. Plenty of compartments, and very well made.