Kensington, maker of all manner of computer accessory from chargers to docking stations to mice and keyboards, has won my heart over with its Contour Balance Notebook Case. This bag is stylish, comfortable, and fitted with enough pockets to keep even the biggest slob organized--and it's well under 100 bucks.
Better yet, it's chiropractor-approved! My aching back was glad to hear that.
The shoulder strap is well-padded and long enough to sling over your head. The inner side of the bag has a special "Air-Flo Contour Panel" that hugs the body while dissipating heat--the bag still slipped around a bit while I was walking around the city, but in general it was pretty comfortable. After awhile, I felt some strain on my shoulder too, but it's impossible to avoid that in a shoulder bag. You can also carry it like a briefcase, and the handles are magnetized so they stick together and keep the bag closed.
The laptop compartment is in the middle of the bag, between compartments for gadgets and notepads and papers. The bottom is well-padded to protect your notebook. The bottom of the bag itself is protected also, with small metal prongs that keep it from falling over when you set it on the ground, and also keeps the bag from getting filthy. This feature is indispensable for those who use public transportation everyday.
There are plenty of thin outer pockets perfect for airline tickets or important papers that need to be accessed throughout the day and two side pockets are ideal for stowing a small umbrella or a water bottle. The bag is water-resistant too, so you don't have to worry about getting caught in the rain (umbrella or not).
The Contour bag fits most notebooks up to 15 inches (the notebook compartment measures 1.6 by 10 by 13.6 inches), and my ultraportable 12.5-incher fit snugly enough that I didn't have to worry about it bouncing around. The bag itself measures 6 by 11.5 by 18 inches and weighs 2.7 pounds. Get yours for $79.99 at Kensingon.com