SEO Keyword Tools
Analyse the importance of keywords like how many queries are done or what the average CPC on a keyword are.
Keyword Analysis Tools
AdSense Keyword Tool
Probably the best tool for analyzing keyword potential.
Search Metrics
Get free data on the quantity and quality of search queries on Search Metrics.
SpyFu
Rate search query importance or get new suggestions for keywords with SpyFu.
Google Insights
Google insights provides you with very detailed data on short-head keywords. You can limit the results by region and time.
Google Trends
Compare search queries and analyze search trends with Google Trends.