Everyone interested in real estate should take a look at Zillo.
According to the Wall Street Journal:
[It is] a new, well-designed, free online service for finding the value of a home that doesn't require you to identify yourself or to communicate with an agent or broker, and provides heaps of information directly to consumers.
Zillow uses data such as tax records, sales history and the actual prices of "comparables" -- homes in your area that are similar to yours -- to come up with an estimate, which it calls a "Zestimate." It backs up the estimate with lavish data -- aerial photos and maps showing prices in a neighborhood; loads of charts and graphs displaying historical data and price movements, as well as details on the size and room totals of a home. It even allows you to enter information, like the types and prices of recent renovations, that might change an estimate.