I only recently upgraded my gear (to a Canon 40D + 2 lenses) so I'm sort of using a temporary bag. It's an over-the -shoulder Samsonite camcorder bag from Walmart.
I wanted something cheap and small so I could cart my essentials on weekend jaunts without feeling like (1) I have a huge bag to travel with, and (2) all my eggs are in one basket. When I get more lenses and accessories, I will upgrade to a "real" camera bag or backpack, but for now, my little shoulder bag works just fine.