The problem with the cheap backpacks (and even some of the more expensive ones) is that they are not totally water proof. I sweat through most of them and have sweaty clothes when I get to work.

I'll throw out a recommendation for the Camelbak MULE IF it fits your laptop. It'll fit m7 13 in Macbook just fine, no idea about a 15 in though. I got the newer version, with Camelbak's new airflow system, basically a few pads touch your back, then an inch or so of open air/mesh, and then the backpack starts. I have been more than happy with it so far.

After some searching, I was able to find a store that carried many of these bags and I went to look at them. First of all, many of the bags are not completely waterproof, i.e., while the items inside will stay dry, the outside of the bag will get wet under the rain.

Chrome turned out to be too bulky. Plus it's made in China. MissionWorkShop was great, especially the expandable Rambler, but I'm not sure a $250 price tag is necessary for a bag. Ortlieb was nice and I was very surprised to find out that they're made in Germany. That's a huge plus and I know the product will probably last a lifetime. Ortlieb Velocity didn't seem large enough to easily put in shoes, laptop in a sleeve, clothes, and books. Even Ortlieb Packman Pro 2 seemed small.

I am down to two choices now: Ortlieb Track 27 or SealLine Urban. The problem with SealLine is that there is no way for me to see it before I buy it and was wondering if any of you could share some picture of the inside. It's great that it's made in USA, but at the store I went they said they had heard cases of SealLine tearing, while Ortlieb is solid. As far as price goes, the Ortlieb is $30 more ($120 vs $150, delivered).

I have a medium size detuer bag that works well for what you want. but be warned thats going to be a fair amount of weight on your back.