I have two backpack style bags, one waterproof, that I would always use for hiking or for extended periods when I'll be travelling carrying the camera rather than using it. But these aren't very convenient for using the camera. For other times when I'm primarily using a camera, such as when I'm shooting a wedding, I want an over-the-shoulder bag. I've recently bought two bags from Ape Case, one larger one that can also carry a laptop, and one a bit smaller. I haven't used these in anger yet, but they seem to be generally pretty well thought out and I think they'll do the job. When I'm going out in a dubious area and want my camera with me, I generally use a cheap lightweight generic and totally unpadded back pack. To protect the camera (I'm talking about a DSLR here) I put a neoprene laptop sleeve inside and store the camera in that. It works really well to protect the camera, and leaves room inside the bag but outside the sleeve for all my other junk. And no-one would guess that there was a camera inside.
Canon 5D & 7D (both gripped), 24-105L, 100-400L, EF-S 15-85, 50 f1.8, Tamron 28-75, Sigma 12-24, G10, A1+10 FD lenses, tripods, lights etc