In this field, I think google has well done than yahoo. google has free keywords analysis tool and traffic estimator based on its database, which can really help advertiser.
One thing that is worth the time looking at is the Microsoft Add-in for Excel. It really is good showing fresh queries on the ad platform for M$. Can't beat that! Here is the link: http://community.microsoftadvertising.com/forums/11.aspx. Spoiler alert: this is pretty much only for advertising.. nothing included to or including results from organic search traffic data. Yahoo hasn't had anything much for awhile.
MSN has some good stuff. Also, try SEMRush. Unfortunately, Yahoo has been gutting their own tool warez, and may be dropping Site Explorer too I'm sad to say. Just a shell of their former self as far as resources go. Google's tool (including Google Editor) is still the best though, not much point in using others as far as SEM baseline research goes.