I still chuckle thinking back to the hilarious A Walk in the Woods: Rediscovering America on the Appalachian Trail by Bill Bryson. His outrage at finding out he needed also buy a “pack cover” along with his new expensive pack is something to which many can relate.
The new Arc’teryx Naos packs are getting good reviews.
Arc\’teryx Naos 55 Backpack 3420 cu in – Men\’s Cobalt, Short
besthike.com 
I use a smaller one – a bit easier to use perhaps? It has a waterproof zipper that opens all the way from top to bottom, so I can put my camera gear in it. It’s great for a day hiker, in case it rains, and I bring it along when I go boating or canoeing. Check out the website – http://www.demardesigns.com