I have a
Canon backpack. It's big enough to carry everything I have and fairly comfortable. I bought it because it was cheap; $35 w/o the tripod they're offering with it now. I like it for what it holds and how it keeps my hands free.
I also own a smaller non-camera backpack I adapted for use as a camera bag. I like it because it doesn't scream "Camera bag!" and holds my camera with lens atteched and 1 extra lens.