Rentometer is a useful mashup, one that's part scientific, and another pure speculation. The idea is simple: just plug in your ZIP code, the size of your dwelling, and how much you're paying, and Rentometer will cross-check your price with local property listings pulled in from parent company iiProperty. Results show up on two screens, one that's a little bit like a speedometer, and another that's simply a Google Map with nearby property listings.
This is a great service if you're apartment hunting, since you can see if the price is higher or lower than others in the area. It's also helpful if you want to see if you're getting a deal, or paying too much for your current living situation.
Of course, the system is inherently flawed, since landlords and property owners who get wind of this system can jack up their rates accordingly. Likewise, it doesn't take into account things like parking spots, security, and whether units are standalone, or part of complexes. Also, newer buildings, and units with more square footage can sometimes create huge price differentials, even on the same block.
The service has an open API for enterprising real estate or rental Web site owners who want to add cost context to their property listings.