One of the tools i use when checking if a domain name worth a buy is estibot.com

estibot provide us with a free, informative and effective tool for checking all kind of aspects of a domain name.

information about google results frequency, times the words shows in page titles, URL, number of links to that domain, ppc bids and much more. some times the appraisal itself, i mean the Appraisal it shows is kinda strange, but it gives you good idea of how the domain will act online when developed or parked.

estibot.com also have premium services for low price to let the professional domain traders to do bulk cheks for many domains and more..

a great tool for sure
check it out