Good hiking camera pack

So hopefully I'm going to the Smokies in July.

I have one camera backpack. It has a bottom compartment for the camera and lenses, and a top compartment that's large enough to stow some water and my rain gear for the hike, and straps to hold the tripod. Unfortunately, though, it's bulky and hard to get to equipment fast.

I also have a slingpack that holds about two lenses and the camera, cards, batteries, ect. No room for extra hiking stuff or tripod. It also, being a sling, doesn't like to stay in place and tends to migrate from across my chest towards my neck, which irritates me. But it does have the benefit of giving easy access to my camera and lenses.

I'm hoping to find something before the Smokies that may be a happy medium of both. Any suggestions on good camera backpacks with easy access to gear? Possibly with a little extra compartment to roll my rain gear and stick a bottle of water in?

Thanks all!

Cara-
I'm not sure if their stuff will be available yet, but take a look at Clik Elite's packs. They are just coming on the market, but I'm very excited about what they're doing. Here's a link to my article about them from PMA:

Clik Elite - Backcountry Camera Packs

The key thing for me is built-in hydration. Carrying water bottles is ok. But I'd much rather have a hydration bladder so I can just drink as I'm walking / riding / skiing.

Thanks John! I googled a bit and REI has the small and large model, but I'm drooling over the medium one they don't have! :)

I'll ask my son when they'll get them