Yes, sure you can also sell your domain name before you get the value for your domain ..... because it is useful to sell your domain name and to assess the value of the domain.........
The best place to get the value of a domain name , visit this site
http://www.zippozap.com/ , it provides the best domain name appraisal value and also you can either appraise a single domain name or upto 10 domain names in a single shot.