How about Kinesis? http://www.kinesisgear.com
Their modular system has proved very useful for me. I was able to carry a pared down 35mm system for my wife, my Mamiya 6 kit, and a 3-lens 4x5 kit (with several graphmatics and tons of 120/4x5 film) with me. Do I in retrospect wish I'd only brought the Mamiya? yes. But it was nice to be able to bring all that gear and be able to separate it out as needed. Whenever I wanted it all, I brought the pack. When I only wanted the Mamiya (which all fit ain a very small bag), I could either put a strap on the bag, carry it on the belt, or keep it in the pack (with a nice 3-liter water bladder which came in handy quite a few times... nice for the plane trips too).
Anyway, it worked great for me, and I can't do anything but recommend it. Probably not the cheapest route by the time you get all the little bags for inside the pack, but unlike most packs you can access your gear and keep the bag standing up (which it does pretty well by itself).