BuyDig offers the Wenger SwissGear Maxxum 15.4" Laptop Backpack in Blue, model no. GA-7303-06F00, for $29 with free shipping. That's the lowest total price we could find by $28. (For further comparison, we saw the bag in another color bundled with a 16GB microSD card for $43 in March.) It is suitable for most 15" and 15.4" laptops and features a padded computer pocket, shock-absorbing shoulder straps, air flow back padding, quick pocket, essentials organizer, adjustable chest strap, and iPod/MP3 pocket.

Update: The price has increased to $29.95.