Microsoft Ad Intelligence
Many of us are frustrated by the unreliable data provided by the Google AdWords Keyword Tool, Google Search Based Keyword Tool, Google Insights For Search, etc...
Microsoft provides a little known tool called Ad Intelligence which provides actual search numbers from Bing.
One major downside, at least for me, is that the tool requires Microsoft Windows and Microsoft Excel. My notebook is Microsoft-free and I am very happy with that. If you're not so intense as me, you can download a free 60-day trial of Microsoft Excel here.
I'd love to see some reviews from people who are willing to infect their PC's with Windows. :D