Likely this data comes from google's keyword tool, which has a paid API. semisla...

		adamgordonbell on April 26, 2010 \| parent \| context \| favorite \| on: Top 50,000 paying Adsense keywords (purchased from... Likely this data comes from google's keyword tool, which has a paid API. semisland.com/semrush.com has alot of good data of this type. Also, they scrape the ads and organic rankings for a ton of keywords.