The good folks over at listing-scouting site RentHop have devised a pretty ingenious tool for use when scouring map-based listings. Their Rental Heatmap function will appeal to deal-loving lookers by allowing users to visualize median rents by neighborhood: the lighter in color a neighborhood is, the higher its median rent against the city's. Likewise on the other end of the color scale: the darker in color a neighborhood is, the lower its median rent against the city's. The same function is available in a year-over-year viewing option. The site also allows users to compare rents for different floorplans over time, and identify median rents and percentage of change in neighborhood rents. Compulsive lookers be warned: it's all free.