Free and best way to Check Duplicate Content

After the updation of Google Panda Algorithm in 24 Feb 2011 the basic scenario of panda algorithm is to unique content is the first priority of any website and the second one is if any website have broken link then it could be penalized by Panda Algorithm. And you could drop your ranking. So After Panda Algorithm you can't use duplicate content in your website. Your Website Content would be 100% unique then you could compete your competitors otherwise you are wasting your time to promote your duplicate low quality Content.