It really depends on your budget, I recently Purchased the Clik Elite Medium Nature Backpack. I am extremely satisfied with it, the photo compartment is just the right size, room for a body with lens attached + 2 or 3 more lenses depending on the arrangement and size. A side pocket with strap is designated for a tripod too.
It does also have a sleeve for a hydration bladder, the specs claim that it will hold 70 ounces, but I purchased the 70oz. camelbak bladder, and when full it did not fit well. Assume a 70oz bladder with 60oz in it will work well though.
The backpack also has a really nice system to adjust it to fit you very well. Plus you have the option of connecting a chest harness for your camera directly to the bag.
Overall, the quality and design are excellent; the biggest downfall is the price, it is around $200.
I ordered from adorama.com and have had fast shipping (free) and a really convenient return policy if you decide you want to swap things around. I really stand behind them for online photo gear.
CE401GR Clik Elite Medium Nature, Photographers Back Pack with Padded 450 c.i. Camera Bay & LadderFit Harness System, Gray ----ALSO AVAILABLE IN BLACK
-LiveStrong