An appraisal can be a very useful tool in the negotiation process, it's the only reason I would consider obtaining one. If this is what you want to use it for, I suggest AppraiseDomains.com. They offer 3 appraisals in 3 classifications;
The CMV is the amount which would be considered fair if neither buyer nor seller are unduly motivated.
The PMV is what you may expect if your name were to meet up with ideal market conditions (e.g. non-trademark infringing and essential for particular market) .
The SSV is the Suggested Sales Value. Though the final sales value of the domain name depends on a variety of factors, our Suggested Sales Value has proven to be effective when attempting to agree on a domain name's value by both buyer and seller.
And NO, I'm not affiliated with this company, Afternic was using them for a while and I purchased about 6 of them, 4 of which have sold.