I never really use Overture....
As far as any free tools I have ever used for Keyword analysis, it would be:
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http://www.seotoolset.com/cgi-bin/checktraffic.cgi For estimate of Keyword daily search activity
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http://www.widexl.com/remote/search-...d-ranking.html For checking a Domains Keyword ranking.
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http://websitesubmit.hypermart.net/keywordanalysis.htm For checking a web pages Keyword Density.
I recommend using the paid version of Keyword Discovery, However using the 3 free tools I listed above together has proven to be rather effective as well.. Just not as detailed with its outputs & diagnostics.
Enjoy....