You may have discovered some of these already. I have been doing alot of KW research lately for some domains I am trying to buy. In doing so I have come upon some tools that I think are pretty cool. Hope I am sharing at least one that you have not discovered and find useful in your SEO efforts.
This one calcs the approximate # of searches on Google instead of Overture.
Not certain exactly how accurate it is yet, but I like the fact that you can check for typo KW and singular vs plural which you can't do on Over.
This one generates a huge list of all the mispellings for the KW you enter.
I'm sure you all know about this one. It's great if you don't have a Wordtracker account since it gives Overture and WT counts.
www.goodkeywords.com is one of my tried and proven all time favs, for many reasons.
Got any cool tools you care to share???