Adventures in Home Brewing.
http://www.homebrewing.org/Home-Brew-Kegs_c_223.html
They probably have the best prices around and ship fast/cheap. Check out their "loose handle" kegs. A little Gorilla Glue and they're good as new! If I need kegs, I check craigslist first, then AHB. I usually end up buying from them though.
I've bought 6 used kegs from them and only had an issue with one. They paid return shipping and sent me a new one as soon as they got the return. I think shipping cost me $12 to Illinois from Michigan when I buy from them. Not bad!
They've got tons too! I called and asked, and the guy told me they've got more than he would ever want to count...