JanSport Endeavor 8000 Pro

Big mountain pack that is lightweight.

A big mountain pack that is ideal for Rainier, Denali, South America, Himalaya, etc. One big compartment with a top lid that converts to a small day-pack. Very strong pack material at a light weight. In a storm you can cram everything into this pack without having to think — it will also accept a ton of stuff lashed to the outside (side straps). When you are cold, exhausted, and fighting a howling gale, you want this pack.

I've used it backpacking too — it carries loads very comfortably. No load sag, no pains in the shoulders, as the hip belt works as it should.

It also skis well, and it is nice for alpine rock routes in the Sierra too (the top lid is nice for grade II-III or even IV rock climbs in the backcountry — it will hold water, food, and windbreaker for a day).

The only caveat I can find has to do with the two aluminum stays—they are not easy to remove, therefore, it is hard to shape them to your back.  

The Endeavor Pro is the kind of pack that should still be made — it is a worthy successor to the venerable (and rare) Jansport 'Alpine Phantom' pack (as used on K2 some 30 years ago).