I think u have to do a keyword research in adwords tool in your niche.then select the keyword as your forum name. eg : webmasters-world
if you are searching on godaddy, it gives you other possible names that you might like in case the domain name that you were looking for is already taken.
http://www.problogger.net/archives/...me-brandable-domains-vs-keyword-rich-domains/ Video tutorial - http://www.youtube.com/watch?v=Ydr3746afcU Hope this help.
You will find some keywords related to your niche. Try that or you may include : keyword-<your company name>