I just bought a Timbuk2 ("Commute" style) for my Al 15" and it's great. Waterproof lining is what sold me. I always seem to wind up having to walk for a half hour through torrential rain with my electronics, and there was no way I would trust my PB to any non-waterproof bag.

The bag looks really cool and has lots of smartly designed pockets and pouches for accessories. The one drawback is that it doesn't come with shoulder strap padding, but Timbuk2 makes add-on ones that match the bags.