http://www.PPC-Mastery.com/
How to find Pay Per Click keywords for Google Adwords by using your competitors PPC ads. Pay-Per-Click is also knows a PPC and Google Adwords is just one of the PPC services available there is also AdCenter from Microsoft and Yahoo Publisher Network YPN.

Google Adwords, Microsoft AdCenter and Yahoo Publisher Network YPN are the big 3 in the Pay Per Click game and this way of researching PPC keywords works for them all.