- The free Copyscape service for finding copies of your content on the Web by typing in the address of your original web page.
- The advanced Copysentry service provides comprehensive defense for an entire website. Copysentry automatically scans the web daily and alerts you to copies of any page on your site.
- The Global Web Rights campaign provides tools and information for "defending yourself against content theft and copyright violations on the web."
In a bit of a 'terms of service trickle-down effect', they make it clear that "Use of Copyscape is subject to Google's API terms". And their FAQ states that "Google has generously provided us with a high-capacity Web APIs key for use with the Google Alert and Copyscape sites" [emphasis added].
(I ran across their service this week when it was used to verify some plagiarism.)