Turnitin - Turnitin is preferred by educational institutions around the world for preventing plagiarism. Instructors at all levels of education can request that students use the service to submit papers, and Turnitin checks those papers for plagiarism.
Unicheck - The plagiarism checker Unplag scans across the internet, repositories, open sources content and databases. It delivers real-time results and has no cached data.
iThenticate - Prevent Plagiarism in Published Works
PlagiarismSearch - PlagiarismSearch is online service that detects plagiarized content.
PlagScan - The Internet makes plagiarism a bigger problem than ever.
Copyscape - Copyscape is a free plagiarism checker.