Bags, Briefs, Backpacks
All -
I'm currently using Lands' End's "Vertical Briefcase" bag. It's a "three-in-one" bag - which can be carried by a handle, shoulder strap, or used as a backpack.
It has a built-in padded sleeve for the laptop, a cavernous main cargo compartment, flap pocket, smaller "pouch" pockets with zippers - perfect for holding my CD Walkman, or a small pad/planner, plus enough smaller pockets for pens, ID's, Palm Portable Keyboard, PDA and/or Blackberry, as well as a water bottle holder on the side.
It holds enough that I can even fit a couple of changes of clothes into it - including workout wear for the gym.
I believe it goes for around $60 - 70 and can of course be monogrammed.