There are a number of sources for this data, including your county's assessor, who typically posts the data on their website. Another source of estimated values as well as recent sales is zillow.com. Finally, you may want to work with a qualified real estate agent who can not only provide comps but help you to conceptualize them. MLSonline.com is an adaquate source to search for homes in the United States, is user friendly, and has many different key qualities to choose from (ie. # of rooms, garage, fireplace, etc). Their URL is
http://www.mlsonline.com/Default.aspx. If you don't own a computer, you can get access to one at a public library. Otherwise, the local Sunday paper is a good source for property sales.