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.
I am still chuckling over your 'Buttstimate' comment. Zillow is an 'OK' tool for consumers to at least get a general idea of things going on in their community and find local values but is definitely not an authority or a basis for an appraisal.
Besides doing your 'Buttsimate' you can also check with some of your local title companies as many have access to the software and online tools for getting a more accurate value as well as a list of comps and recently sold properties. They use these tools to market to realtors to use their title company. It may not be 'free' depending on the company, but I know if I had an investor who was sending me deals regularly I would be glad to pull him or her a comp and recently sold report for a potential investment they were looking at. It is all about relationships, and I know I work hard to help my customers and clients achieve their goals through such services.