I second the plug for Waterfield Designs. I love my Cargo Mambo Combo.
(http://www.sfbags.com/products/mambocombos/cargosuite.htm)
The stuff is unbeatable. I wasted a lot of money on other bags before I found them. Theirs are amazing quality, their customer service is better than anything you'll find around these days, and all their bags are made in the U.S. Their sleeves fit like a glove. I rave about them to my friends, and I'm not usually like that.
6 Great Bags for Your iBook or Powerbook