Duplicate Content Tool
http://www.duplicatecontent.net/

This tool takes into account two parameters when compaing URLs: it considers the similarity degree for both textual content and HTML markup. This allows you to check whether two texts are substantially similar and the alikeness of the structure of the pages. You get mainly two pieces of information from the analysis: a) Markup similarity – They consider how many HTML tags are found in both documents: this gives a measure of the probability that two layout will be considered similar or identical to each other; and b) Text similarity – This value gives an estimate of the risk that any textual content might be filtered out by the Duplicate Content filter. This has been added to the tools section of Research Resources Subject Tracer™ Information Blog.