I use the Targus Sport notebook backpack (http://www.targus.com/us/product_details.asp?sku=TSB215) with an Incase sleeve with my 15" MBP. The backpack is great for my needs, but its definitely designed to hold more than just one textbook in addition to the notebook, so it might be too much for your needs.
Still, it works great at protecting the notebook, while hiding the fact that you're carrying a $2k+ notebook around with you. Also, the bottom of the backpack is PVC and designed to repel liquids, which has come in handy a couple of times when drinks have been spilled in my classes.
Still, it works great at protecting the notebook, while hiding the fact that you're carrying a $2k+ notebook around with you. Also, the bottom of the backpack is PVC and designed to repel liquids, which has come in handy a couple of times when drinks have been spilled in my classes.