Have a look at this: http://boardingarea.com/blogs/flyingwithfish/2009/10/14/511-tactical-rush-24-backpack-a-great-multipurpose-travel-companion/
Or though it's a tactical bag and not designed for putting cameras inside it it's tough, has lots of pockets and it doesn't make people think you are a photographer but rather a camper so stealing your bag won't seem so rewarding to them. A good feature if you are traveling to certain places.
There are other great bags from lowepro, thinktak, tamrac, crumpler, etc but many are expensive and scream camerabag.
If you like the idea of tactical bags there are many companies. 511, Maxpedition and blackhawk are some of them.
I'm planning to buy a 511 rush 72 backpack and put a lowepro toploader 75AW inside after I buy my DSLR. That might happen sometime around July-august so don't expect a review from me until then.