Robin Good: PlagSpotter is a free web service which allows you to rapidly identify which specific sentences of your articles have been duplicated elsewhere on the web and at which specific URLs they have been republished.
After analyzing a specific URL, PlagSpotter presents you with a report, that includes a copy of the text published at the URL you have specified, in which the sentences that have been duplicated elsewhere, havebeen highlighted.
By clicking on any of the highlighted sentences you can get a list of the URLs where that specific content has been duplicated.
From the official site: "PlagSpotter is an online duplicate content checker that allows users to put their webpage URLs in to start an Internet duplicate content scanning and detection process.
The user can get a list of sites that duplicate the original source by displaying excerpts of the plagiarized text in a sentence by sentence format."
Free to use.
Try it now: http://www.plagspotter.com/