Ergon BC3.

I bought it due to it's claim of being: waterproof, having room for a hydration bladder, and relatively large size for a cycling backpack.

It's not a rolltop, nor does it have a liner, so it's claim of being waterproof was pretty suspect when I bought it. I paid $200 for it (kind of silly looking back...), but I rode in a torrential downpour (complete with hail!) and water managed its way into the pack. I was surprised though, it didn't seem as if it came in through the zippers, which is where I assumed it would leak (due to lack of a roll-top), but from the bottom, where I can only assume a puddle accumulated in the outter elastic "pocket," and leaked through, somehow.

Only a little bit of water came through, which is pretty impressive. It was really coming down there.