Go to your SE and type "Keyword Tool at Google Adwords"
. This is a neat utility program provided by the industry leader itself - Google, it allows you to generate keywords based on descriptive words and phrases or based on your website content.
On the same "Keyword Tool at Google Adwords" website, you can also try the Search based Keyword Tool, a new utility program that will generate ideas matched to your website and based on actual Google search queries. Enter your website name and the program will generate matching keywords! The method sure beats guessing for keywords.