You didn't say how much you have to spend or how big of a hurry you're in but if you've got some time and a limited budget I highly recommend a trip to eBay before you buy anything.  There's usually a pretty good selection of bags there and they can usually be bought for very little money.

As for a recommendation, I have a Belkin bag that I really like. Unfortunately, I don't have any of the paperwork with it anymore so I'll tell you want I like about the bag since I don't know the model numbers.  It has:

  - nicely padded straps
  - lots of conveneintly placed pockets - they make grabbing a pen or cellphone easy
  - two completely seperate compartments - one for the laptop and another for my books.  This makes it easy to remove either the laptop or my books but doesn't require that I remove both to get one or the other.  Most of the "bookbags that hold laptops" just have a padded divider in the main compartment.
  - a well placed pocket for my a/c adapter
  - a top mounted handle
  - although I've never submerged the bag it has kept everything inside of it dry even in the worst of rainstorms (I park a good ways off and sometimes get caught in the elements)
   - a design that allowed me to cut off the waist straps without hurting the bag. I think waist straps totally suck but to each thier own.
   - It has a low key appearance.  Some might even call it boring. 

Good luck with your purchase. Let us know what you finally pick out.