Leather, canvas or waxed cotton. It all depends on your personal style, where you live and your office dress code. Keep in mind that lesser quality bags will use synthetic materials (which won't age well) and thinner fabrics which can often fray or tear. Look for quality stitching and solid hardware.
Do you need a bag that can stow your lunch and gym clothes along with your laptop? Or something sleeker to house your iPad and a few files? If you commute on a bike or do a lot of walking, you might be interested in a refined rucksack. Gadget lovers should opt for plenty of pockets.
A bag can practically last forever, if you keep it in good condition. That means checking the stress points like base corners, hardware and straps for wear, and cleaning it every few months. Condition leather bags and clean canvas with soap and water (but don't throw them in the washer).
Ernest Alexander, $295
Club Monaco, $140
Jack Spade, $245