actually google keyword planner have maximum acuracy and enough options to understand or research the keyword. As Google is the no. 1 search engine every body try to get ranking on Google and same reason behind using keyword planner.
Google Adwords Planner is a wonderful tool. But if you really want to generate a valuable traffic, then i will suggest, Google Auto Suggestion and Google Trends. Google Auto Suggestion: You will find it below the Google Search Result as Suggested Keywords. Google Trends: It will help to understand the trend of the keywords, website and so on.
On top of the Google Keyword planner I have been using Keyword Digger Pro. Not exactly what I thought it was going to be when I purchased, but it helps get the job done. Anybody else tried Keyword Digger Pro?