Backpacks like the Banjo Brothers Commuter pack, Deuter, Chrome, Timbuk2, Camelbak, etc. that are made for cycling will work best. Personally, I do not need or want a pack with a waist belt and sternum strap - the less straps the better. The new Timbuk2 backpacks have nicer contoured thinner straps and I like those too. I find that you do not need a lot of padding if the straps and the pack fit well. Some thin padding against the back helps. For raw capacity the Banjo Brothers bag is hard to beat since it is basically just one compartment and waterproof at that. You can even over pack it because of the flap/strap design. The nicest part of the bag is that you can make it smaller when it isn't carrying much stuff just by rolling it down.

The Deuter packs have a lot of nice bike-specific features like built-in pack covers in high-viz, pockets galore, good layout, daisy-chain loops.

Personally I favor the messenger style backpacks with the flap over the top design - it is really useful for over-stuffing, awkward loads, and if you are lazy, keeping your rain jacket handy. The Baileyworks Citizen looks good to me too.