I recommend the Crumpler 5 Million Dollar Home bag. It looks just like a purse or messenger bag (no one ever guesses that I have an SLR in there) and can fit your camera + an extra lens, plus a couple of doodads in the front, flap and side pockets. It's well padded, sturdy, and the strap is comfy.

I have had one for years, and have been very satisfied.