For free keyword tools you can try Adwords' keyword tool. SEObook also has a free keyword tool (give you suggestions and performance data from MSN, Yahoo! and Google).
For paid research tools there is Word tracker and Trellian although they both offer free trials and free keyword suggestion tools, I don't know what the paid version gives you.
you can go for word tracker, google ad words for doing keyword search or if you have used any tracking tool like statcounter tere also you can get the keywords you can come to know wat type of keyword people search.