I wrote a program that scrapes craigslist to get the GPS information about up and coming garage sales. It converts the information into a GPX file that can be read by Garmin GPS units.
try the Garage Sale Finder GPX File
I am putting the form up for use here and it will stay here until the craigslist people decide to ban my IP.
You can host it yourself if you have PHP by downloading the code:
PHP Source for Garage Sale Finder
There is some interesting Javascript for selecting the craigslist region. The GPX file creation is there for anyone who wants to purpose the program for something else.