Although everyone and their great grandmother has already written about this, I wanted to point out Housingmaps to the 10 people who haven't already heard or read about it.
This site uses the Google Maps UI and Craiglist data and was put together by a third-party developer with no relationship to either company.
At Drillilng Down on Local, we discussed how maps might evolve and various monetization scenarios. Real estate is an obvious one.
Beyond serving geotargeted ads on the same page, Yahoo has monetized its mapping product to some degree with sponsorships — buttons (with a corporate icon) below the map that allow users to find Washington Mutual branches, Hertz Rental locations or Holiday Inns.
In the real estate context, Housingmaps offers real utility to consumers because it allows them to see where listings are and allows them to sort by price or see only those listings in a certain price category. By clicking the icon, you get a pop-up with photos of the property (if photos exist). Unfortunately, the Craigslist data aren't comprenhensive. So this tool isn't a "one stop shop" for home buyers or apartment hunters.
Speakers on the Drillling Down mapping panel wisely cautioned that to over-monetize maps would be to destroy the user experience. However, one could easily see — again in the real estate context — how brokers/agents could pay to feature their logos or links to their other properties (on the pop-up windows themselves). Some would pay to be featured at the margins of a map (e.g., a top performer in a particular area).
In short, there would be a good deal of lucrative, highly targeted inventory that could be sold directly to local advertisers — and there would be contextually relevant (think moving companies) opportunties too. Calls could potentially be monetized as part of this offering as well.
Housingmaps is a novelty that points the way to something much richer and more interesting. Now who's going to build a vertical around it?