Before Zillow.com, I paid nearly $100.00 for access to The First American Corporation's data base of recently sold properties so that I could get an idea of what a property's value was. Of course, I am not a Realtor, so this information was not as readily available to me.
Then came Zillow. This site is awesome for people who are not real estate agents and want to check for recently sold homes in their neighborhood. Some counties have organized their own database, but not here in Gainesville (Alachua County).
I would warn against putting too much faith in the "Zestimate" that Zillow offers for specific properties. Primarily because it cannot consider the condition of the properties or their value based on their exact location. In other words, Zillow will consider the all of the values surrounding your property, even when the neighborhood directly across the street might not be very comparable.
I primarily use Zillow by entering a specific adress and then pulling up 'recently sold' properties surrounding the property. I write down general info such as address, bedrooms, selling price, and square footage. I always drive-by the properties so that I can see which ones are in similar condition and neighborhoods to the property I am comparing. Then I put together my 'Buttstimate". I know, that sounds bad ( just consider my last name).
Here's a recent article about Zillow reported by RISMEDIA.