For the vast majority of my travels I've been using this bag
. It's got a ton of space, and quick access to your camera through the side port so you don't have to take off the backpack to take a quick picture. Only complaint I have is there is no easy way to carry a tripod with it.
If you want something a little nicer looking you could try this one
. It's a bit expensive, and on back order, but they make good bags. I've got their messenger bag, and use it whenever I'm traveling light and don't need the extra space.