My main laptop bag holds so much that I'm tempted to pack a lot more than I need much of the time, and the end result is that my svelte little 12-inch PowerBook G4 ends up being only a fraction of the overall weight I carry. For an outing where I don't want all my gear, or, in fact, anything but the laptop itself, I've just started using a MaxSleeve from MaxUpgrades. It's a sleek black bag made of a dense polyurethane foam, and my PowerBook fits snugly inside. A pair of zippers enable you to close it, and the zippers are on the outside so they never come in contact with the surface of the PowerBook. MaxUpgrades also sent me their iProtect cloth, which is a microfiber cloth you can use to prevent finger oils on your keycaps from marring the LCD screen surface when your laptop is closed; it's also designed to clean sensitive LCD screens without scratching.
Lastly, remember that you can increase your chances of receiving a prize. On the confirmation Web page and in the email confirmation message entrants receive, you'll see a custom URL that you can send to friends and colleagues so they can enter the drawing too. If one of our randomly chosen winners entered using your referral URL, you'll receive exactly the same prize. The more people you refer, the more likely it is that you'll win a prize, so feel free to distribute your referral URL widely (without acting like a spammer, of course!)