I came across this interesting site yesterday call HotPads.
HotPads.com is a map-based real estate search engine, listing homes for sale, apartments, condos, and rental houses.
They have maps for many of the popular cities in the US. Essentially the maps grid all the available properties in the selected area. One of the highlights on their site is the rent ratio heat map.

Red indicates a strong rent area, while blue dictates buying potential. The ratio is basically derived by dividing an area’s median house price by annual rent.
You can also click on the properties on the map to see more information about it without having to leave the site. Other filters to search by include: population density, per capita income, household income, median age, median rent, and foreclosures per household.
How does your area stack up?