My best dogs have come from craigslist. Like Tap's MIL, I have found some purebred dogs that owners had to rehome due to a move. These dogs were loved well, trained, and very well behaved. I still send updates and pictures to the previous owners and when I have had a question about something- they are more than happy to help me out.
Ebay Classifieds is another free classified sales site. You can search by location.