One of the first tools that I found when I was creating a new site about 6 months back was the Keyword Suggestion Tool from DigitalPoint.com.

If you are looking for specific keywords that are in the same niche as the site you are creating, or looking for keywords to include in your site, this is the tool for you. It gives you an idea of how many searches are done per month from Overture(Yahoo) and from Wordtracker.

If you have never used this tool, it is one of the important ones too add to your SEO tool bag. Best of all, it is FREE thanks to DigitalPoint.com