Zillow and Eppraisal.com are two websites that offer free home values by address. Each site offers an estimate based upon values of nearby homes and other real estate data.
Zillow gives an estimate for any home's address based upon known information, such as number of bedrooms and bathrooms and square footage. They also list features of the home and provide a graph showing valuation changes over various time periods.
Eppraisal.com also provides home estimates based upon general details, and it lists nearby home values for comparison. This site also provides the current property taxes and all available country and public record information.