Semrush.com is a great keyword tool for discovering competitors keywords campaigns in search engine marketing (SEM) and search engine optimization (SEO). You can discover from which keywords coming traffic to competitor website. It allow to find keywords which are pretty simple to reach first page ranked in google, allow to find high CPC keywords for adsense and low CPC keywords for adwords. You can get acces for their data from $69, not cheap but for sure worth this price, because will bring much higher profit.
Here You can check for free some very useful website metrics:
Enter domain name bellow and press CHECK button to quickly check all above semrush metrics for free.