Both my boyfriend and I use manhattan portage bags. I have a smaller one, and use a laptop cover (that also has it's own strap for when I use it on it's own) for mine. He has the "computer bag" with a built in padded pouch for his laptop. They're both really nice, well-made, (i believe lifetime) warranty, etc.
The website is:
www.manhattanportage.com
I've been very happy with mine, and they don't cost a fortune.