As HighSierra mentioned, check out wealth of information on ultralight gear at
http://www.backpacking.net/bbs.html. There are quite a few names listed there and you would do well to try as many of them on as possible. As you go to ultralight backpacks you'll find that you are giving up on features that you may feel are required. For example, many of the ultralight backpacks do not have hip belts, external pockets, frame stays, or padding along the back to insulate you from your gear. You may find that the weight savings is not justified by the lack of features.
I use an old book bag type backpack made by North Face about twenty years ago for ultralight loads. I added a waistbelt to prevent the pack from bouncing up when I run and it has held up well to quite a bit of abuse. This pack has no external pockets, no padding except on the shoulder straps, and about 1,500 cubic inch capacity. The total weight is less than a pound. If I'm going on a longer trip, my backpack of choice is the Osprey Aether 75. It weighs two to three pounds less than competing packs and is quite comfortable fully loaded.
I would also suggest that you consider a custom or semi-custom made pack. McHale packs are supposed to be very good, but I think they are likely to be overkill given your limited needs. Also, the Osprey Aether series is very good