The Elemental Horizons Kalais is one of the packs I would look at if I needed a new one (which I don't). The others would be the ULA Circuit or Ohm.

The pack I bought in early 2006 (the then just-discontinued Six Moon Designs Comet, with the optional stays) still works fine. I added a hip belt pocket and a shoulder strap pocket, trimmed some extra-long straps, and ended up with a 29-oz. pack that will, even for me, comfortably carry about 30 lbs. I had a bit more than that for a couple of days; my shoulders and back were fine but my knees and feet protested. Some stitching came apart its first summer, but SMD fixed that for free and I have had no more problems. I do treat this pack very gently, because the lightweight fabric is definitely not bomb-proof.

Six Moon Designs is another company that has discontinued its really light packs and gone to sightly heavier models. At least their packs are still lightweight.