I use a Lowepro Slingshot 302 AW Backpack. I can't say enough good things about it. It holds all the gear I need when out shooting and is comfortable to wear. I always carry a tripod with me for the HDR shots so the tripod mount is great and easy to access.
The last time we were in New York City I'm sorry to say that the zipper broke. OK, what to do. I contacted Lowepro through their website offering to mail the pack back to them for repair. Within an hour or so I got an email asking for some additional information. After a very short while another email came telling me that the would replace my slingpack at no cost and that I would have it in a few days. It just arrived. How great is that.
Offering a great product and with service like that, Lowepro has a customer for life. I'll pass this information on to my photography club. We have over 200 members.