My listings are on Realtor.com, Trulia, Zillow, Oodle, Homefinder, and several others plus the sites that they feed out to. I've been doing a lot of marketing on Facebook, both through my fan page and through ads. If you hone in your target market by age group, education level, etc you should get some good hits. I've also had good results from marketing my open houses the same way, as well as posting them on Craigslist.
I also agree with Carol - marketing to agents up here in the frozen tundra is a great idea. There are lots of people here who own vacation property in Florida and lots more thinking about it with the prices in today's market.
I'm in Rockford, IL, just north of where Carol is, about a half an hour from the Wisconsin state line. I'll also keep it in mind! Can you send me the info? I'm with Nextage Professionals. My email is firstname.lastname@example.org and my phone is 815.621.2826