Check out the Case Logic SLR/Camera + Laptop backpack
. Just got it to hold my 500D, laptop, accessories, and lenses and I have been really happy with it. It can hold a lot more than I have in it right now. Very modifiable inside to fit whatever lens you want to keep on the body and good design to allow quick access to your camera at all times. Also has an exterior strap if you travel with a tripod. As an added benefit, the name and look don't scream "Expensive camera in here!", so a bit of added security there. Good luck with the search!