Vanguard UP-Rise 45 - £80/$140
Some clever trickery has gone into the design of the Vanguard UP-Rise 45. Not only does the backpack feature a partition for separating the camera kit area from the upper compartment for everyday stuff, but you can move the divider up and down to make more room where you need it most.
There's also a large, separate front compartment and, if you still need extra room, a handy zip enables the bag to extend in the same way that's often used in carry-on luggage bags. This gives you an extra 6cm of depth in the camera compartment for unusually bulky lenses.
The camera section opens at the rear of the backpack, but there's also a quick-access opening at the side, enabling you to grab your DSLR and whatever lens is currently attached. The opening is sealed with a zip, Velcro panel and a locking clip, which appears to be a belt-and-braces approach, and then some. Despite all this, however, the seal isn't good enough to keep out grit in a dusty breeze.
There's a full range of additional features, such as a waterproof cover, tripod fasteners and waist belt, all of which stash away neatly into pockets in the bag's overall construction, so they're kept tidy and out of sight when not in use.