I use 2 backpacks, a LowePro Mini Trekker and a LowePro Photo Trekker AW. Both are good for different reasons. I have a friend that has a Tenba backpack and it has a 2 compartment system like you are looking for. The top is like a regular lined backpack for clothes or lunch etc., and then the bottom unzips and opens up to a camera compartment good for a few lenses and camera body. I can find out exactly which one it is if you're interested. I know that out of 3 or 4 bags this fellow has it's definately the favourite one.