Google's Keyword Tool can be used to get new keyword ideas for your Pay Per Click advertising campaign or for optimising your website for search engines. Enter a few descriptive words or phrases, or by typing in your website's URL.
Read more at https://adwords.google.com/select/KeywordToolExternal
If you're looking for more keyword ideas you could also try Google's Search-Based Keyword Tool, that generates ideas matched to your website. It's based on actual Google search queries and is matched to specific pages of your website with your ad and search share.
Read more at http://www.google.com/sktool/
Updated December 2009