One is to go to a site like Zillow.com, they can give you a general idea of how much homes are worth in your area. If you are buying a home to live in, this can be okay, but it is not terribly accurate so if you are doing this for investment purposes I don't recomend relying on those sites. The other way is to search the county tax records for your county. You will be able to see the sales date and sales amount for homes near the property you want to establish value for. Tax records, however, are limited. You won't be able to get important information about the properties, such as number of bedrooms, square footage, and amenities that heavily influence a properties value.
Of course, I recommend working with a realtor. They have access to a central database of homes for sale and sold that only realtors can access and it is the most reliable way to establish home values.
You don't mention whether you are purchasing a home to live in, or as an investment property. Either way, your best bet is to form a relationship with a realtor who can give you accurate information to establish home values.