WordTracker is good - You can even sign up for a free trial. Other than that, there are plently. Google Sandbox, Overture to name some.
I suggest you use a combo of both these keyword research tools at once, since Wordtracker shows you results relating to the current Internet environment, whereas Overture shows you what was being searched 3 months back!
google Adwords keywords tool https://adwords.google.com/select/KeywordToolExternal yahoo overture http://inventory.overture.com/d/searchinventory/suggestion/ Adulu yahoo global keywords http://www.adulu.com/adulu/keywords/
Try this tool from Digitalpoint digitalpoint.com/tools/suggestion/ To get details for Google Multiply traffic in US with 10