I tried www.domaintops.com on a few domains, it seemed rather accurate when done properly. (E.g. Exporting.tv for $12, was actually sold at $10) Seems a lot better than those like LeapFish, Swift Appraisals, etc. Could be a useful resource for appraisers here? I'm interested to know if I'm alone with this opinion.
I use DNscoop. It's good to check PR and backlinks of a domain, but I'm not sure if the appraisals are accurate.