Copyscape has launched its new premium plugin that allows you to check your blog post and other content uniqueness by searching it on web for duplicate content. The plugin uses Copyscape Premium API for checking the duplicate content on the web so you should have a premium copyscape account to use this plugin in your WordPress install.
SiteLiner.Com is another free service by CopyScape which is the most popular search engine for checking your content against plagiarism and duplicate content. Copyscape only checks for duplicate content between a single page and the entire web, but due to many received requests, the company created thus a tool that can detect duplicate content within one website only. SiteLiner.Com simply allows you to explore your website and check duplicate links, broken links, internal page ranks and much much more. Visit its Home Page, type your website address in text box and press GO button.
WordPress Plugin Repository has a new WordPress plugin called Changes. It checks your WordPress blog postsagainst the original content and provides you the percentage of changes made.