I keep mine in an Incase Sleeve inside my backpack. I was using a messenger bag, but the messenger just couldn't hold everything I was looking to carry around. I'm still on the hunt for a bigger one!
in a cheap messenger that I love, a Dickie's Deluxe DJ bag:
The sleeve was actually more expensive than the bag!
The sleeve BARELY fits in the bag, not a lot of extra room, but enough for some files, the laptop, power adapter, external 2.5" drive, and a mouse. This bag also has a zipper on the front flap for some extra stuff, a second zippered compartment inside (this is where I put the power adapter and mouse), and slots for 4-5 pens. I think I paid $33. It's a steal, and very tough.
There are many nice backpacks for 15" inch laptops. Some not very bulky ones (very important for me and others who spend a lot of time in crowded trains, bus etc). Unfortunately that is not the case for the 13" macbook
Im using the incase sleeve along with a northface jester backpack. Little expensive but I really like the shoulder straps. Had it for a few years. Pretty sure you can get it for cheaper now. Lloyd
It's not that it was awful, but when you price it against the Tom Bihn, spending the extra money gives you a sleeve in a whole different category. The Incase protects against scratches and maybe dropping it six inches, the Brain Cell can take a drop from a couple feet without any concern.