The web is growing everyday and avoiding plagiarism against copying of original content without permission get more importance. Anyone surfing over Internet can copy your content and instantly paste it onto their own. To avoid plagiarism I'm going to recommend a free service that shows whether your content is copied.
The free services of Copyscape allows users to find copies of your content on the web. The whole service is free and what you need is to put the URL of your site/blog and start to search for copies.
As with this screenshot below, you can see the result of contents that have been copied.
The best feature of the service is that you exactly can get highlighted those content that have been copied.