Here are some free tools that you can utilize for keyword research.
Free Keyword Term Suggestion Tool By KeywordDiscovery.com - Generates the top 100 keywords related to your entry. Additional results are available with a subscription.
Google AdWords: Keyword Tool - Allows you to generate keyword ideas based on your entry. The results can be sorted by popularity, and exported in .txt or .csv format. You can alternatively enter a URL of a site whose keywords you wish to analyze as well.
Google Insights for Search - Allows you to enter a keyword and see it's popularity during specific time ranges, and in specific regions.
Keyword Density - SEO Tools - Allows you to enter the URL of a site and analyze the keyword density. Good tool to use to make sure you are achieving optimum keyword density on your website.
