If getting a technical backpack is too expensive, or you just figure that you don't need that many features, then you could check the discount bins at your local outdoors store. You might be surprised at what you find, especially if you check last year's models. If manufacturers upgraded their backpacks, odds are that they'll be on sale. The outlet sections at your favorite online outdoors shops might also have some interesting backpacks. Almost all technical backpack companies make some kind of laptop bag.
1. Golla Backpack: This is a stylish backpack, that sells from $30 to $50. It can carry a laptop of up to 15.4". The strong hall loop, and the vast array of pockets of all kind make it a good way to carry your daily gear around. It's also available in some nice designs and colors, from green to pink, allowing it to appeal to people looking for a distinctive backpack.
2. GoLite Jam: We picked up this ultralight backpack a few years ago (2007) and it has served us well as a lightweight alternative school bag. There have been a few newer versions (the smaller Peak or bigger Pinnacle might also work), but you can still find the '06 version at a few different stores for around $50 (we got it free as when we bought an Osprey Atmos 25 and 35 second hand). It doesn't look like much, but it can expand up to a capacity of 50 liters. While the version we had didn't have a dedicated laptop pouch, we used an Incase sleeve to make one ourselves.
3. The North Face Loafer Backpack: This retro-inspired daypack is pretty distinctive and comes in a variety of colors (brown, blue, white, black and purple). It has a 31-liter capacity and its laptop compartment will fit most 15-inchers. It also features a padded phone pocket, with a water-resistant zip. It sells for $89.
4. Osprey Flap Jack, Metron & Momentum: Osprey not only makes some good technical packs, but they also make laptop bags, including these three models. They sell from $79 and upward and will fit 13-15.4" laptops.
5. Medium Control Small Backpack: This backpack was handmade and is available in 8 different colors. It's made out of canvas and will fit most 15-inch laptops. The best part is that it only costs $38.