UofL, google maps already has real estate with that map/mouse-over feature. They need to go ahead and do the rentals too! It is a huge market worth mucho $$$.
oh, wait. They already have that feature! I just checked and they added it.
Go to maps.google.com
type in city or zip in the map search bar
on the map, click the "more" button
select "real estate"
in left side bar, be sure to select "show options"
check "for rent"
map takes a while to upload, but if you click on each location, you get a brief summary, with more info link which includes price, photos, address, directions, parcel map, street view, contact info, and links from google search for this address.
The listings appear to be pulling from at least a few sources, but not all.
click here for an example.