There are a ton keyword tools out there, and supposedly wordtracker is the best, but I think the best way to make the money with the way Google is trying to kill the people marketing with ppc, is a site called hexatrack where you can track certain keywords over a period of time, and see the ads that are consistently in the top 3, so you know they are making money. If they weren't, they wouldnt be bidding the most for those keywords for 3 or 4 weeks straight