a couple o months ago i did a series of posts about creating mini sites, and one of the aspects i menitoned was keyword research like netvestor blog wrote, but in a more detailed post:
Creating mini sites - Part 2 - Keyword Research | Blog dahh net!
but, as many of us, like to have the job effortless, there is a great way to check if the competition and searches/day are compatible to our criteria or not.
I explain how to do this easyly in this post:
Creating Mini sites - Part 3 - GTrends made easy | Blog dahh net!
hope you find them usefull