Another great option is the Gregory Z65 ($250), a top-loading pack with side zippers that let you access gear that's tucked just about anywhere in the pack without unloading. I’ve found the shoulder straps are just a bit on the thin side, but it still carries good loads. I had no problems with the Z65 on a four-day trip into in the Grand Canyon backcountry with two gallons of water. It’s also designed to let air flow across your back, which is a great feature on a hot day.
I've noticed that modern packs have become over streamlined, and you don’t see many with long zippered side pockets like those on my antique, but still serviceable, Dana Designs Terraplane. They were extremely useful for carrying things like telephoto lenses. And what happened to those removable side pockets that tied into the side straps? They were practical, and they used to be universal, but now nobody makes them. I see a product opportunity.