I have a Tumi Alpha T-Pass Business Class Brief Pack, which is no longer sold by Tumi, but still readily available. I got it at a discount as a replacement for my prior Tumi backpack, which they judged as "damaged beyond repair," but would probably not get another Tumi, since they no longer offer a lifetime warranty. I wrote a review of it on this mailing list.
Backpacks are very subjective, so a lot depends upon your budget, style you like, etc. Personally, I like having one with a TSA-approved laptop compartment to speed things up, but that might not be an issue for you if you don't fly a lot.
P.S. Some older posts on Neowin you might enjoy:
What Backpacks Do You Use?
Coolest Laptop Bag/Backpack