What's a reliable Yahoo Keyword Suggestion Tool?

Hi! I'm working on a project for a site that wants to rank on Yahoo and I'm doing some KW research. Is there a recommended Keyword Tool for Yahoo that anyone can recommend? I'm pretty new to this and I'm not 100% sure if I have to use anything other than the AdWords tool.|||No dear yahoo have not any type of keyword provider tool.But many of websites give the facility to find the keyword according to yahoo search engine.|||A1 Keyword Research is one very good option.|||why dont you try google adwords its free and really good