Most people use EstiBot and you can as well. But when it comes to the value of a domain there are a lot of factors to take into consideration. You can learn a lot more by looking up info here at NamePros. Also go over to NameBio and see what recent domains are selling,
When I have a domain I am thinking of buying I go and put the keyword in NameBio and see if any similar names have sold in the past. I also check how many searches the domain gets monthly and one very important factor is to go over to Zfbot and see how many similar domains are owned, these are potential buyers.
- Will