I've been carrying a backpack for so long it's become a bit of a trademark, and I still like my current model, the exceptionally lightweight Kata Bumblebee DL-210. But it's a bit bulky for urban use -- think bull meets china shop -- it's impractical when I need to swap lenses frequently, and I find myself switching to a smaller bag when I don't need to schlep my camera equipment (which I hate doing). So I've begun the hunt for a more practical solution. Thus far the Tenba Mini Photo/Laptop Messenger Bag has proven to be a winner; it's relatively small and light, comes in enough colors that everyone should like at least one, and it's quite intelligently designed.
The bag is made of Cordura Nylon, with a small weave that keeps it from looking too casually rugged. It resists a gentle rain, but I wouldn't take it out in a downpour -- I wish it came with a rain cover. I tested the black model, which turned out to be an unwise choice given my white cat, and in general the bag seems to attract schmutz a little more than smoother, less-dense Nylon weaves or canvas. The inside uses lighter ripstop nylon, and the main compartment incorporates the typical "reconfigurable" padded five-divider system with Velcro flaps that attach to the sides of the bag. I tend not to like these types of dividers, because once I remove them I can never get them back into factory-fresh locations (the larger bags have a completely removable insert instead). But I haven't removed them here as they provide some needed organization for the bag. There's also a padded pocket with a simple Velcro strap for a laptop or tablet.
A dSLR goes into the central divider, lens down, and there are two dividers on either side of the center for flashes, lenses, and other accessories. Two flaps on the central divider fold down to cover the side sections. This comes in quite handy, since it lets you put more stuff (like a compact umbrella) on top of your equipment. Plus, by putting it in with the lens extending to the side over the flap I was able to cram a Nikon D4 with a 24-70mm lens into the bag relatively comfortably.