Aaron Wall of SEOBook made a nice post yesterday about niche keywords. It starts out with the question of whether there is a way to estimate search volume on a niche term that is not highly targeted. It goes onto touch on how the volume of the keyword traffic doesn’t necessarily correlate to the value of the traffic. You can have some very low traffic words that convert like crazy, or where the average value of the customer over their lifetime is high. First, he recommends just going into your AdWords interface to look up a word to get an idea of it’s search volume, then to use his keyword tool to get some variations and costs. Aaron winds down by mentioning HitWise and KeyCompete as closed paid options of filling out your keyword list, and is generous enough to mention HitTail as a way of getting more suggestions based on your existing traffic.