Crumpler isn't known for being super weather proof,at least not like those others. If you're looking for a bag for walking around,all the others have straps that work better with the strap cinched all the way up on your back. Timbuk2 really are the only ones that work equally well on and off the bike. Having said that,I prefer the strap system and pocket layout on the Bailey to Chrome's;that seat belt buckle really is just bling and extra weight. RELoad and PAC are pretty much custom,so you'll pay more and have to wait. I've heard good things about Mission Workshop,but have never seen one in real life.

If it absolutely,positively MUST be waterproof,then I'd suggest SealLine:
http://cascadedesigns.com/sealline/u...er-bag/product

I've got a small(should've gotten the large). They're kinda small(the large would be a medium to anyone else),and the material and closure system don't allow over packing,but anything inside will def stay dry unless you actually go into the water.