Minimal Portability (17 - 18 inches): If you plan to keep your laptop in your home and leave it on your desk or just move it between rooms, a system with a 17 or 18-inch display like the Alienware 17 should be fine. Laptops in this size range are usually the most powerful, because they have plenty of room for heat-generating components. However, they're heavy to carry, a tough fit for most bags and too power-hungry to use unplugged for very long.
Dell Home, via its Member Purchase Program, offers its Dell 15.6" Laptop Gaming Backpack in Black/Red for $28.49 with free shipping. That's tied with our expired mention from four days ago as the lowest price we've seen for this bag. (It's the best deal we could find now by $20.) It accommodates laptops with up to 15.6" screens and features a shock-absorbent EVA molded front shield, adjustable shoulder straps, and a deployable rain cover.