Plagiarism Online Check

http://www.plagium.com/

I like this.
http://www.copyscape.com/

http://www.duplichecker.com/
http://www.dustball.com/cs/plagiarism.checker/
http://www.crossrefme.net/
http://www.articlechecker.com/

This has text limit.
http://www.plagiarismchecker.com/

This helps you do essays. Students posts while graduates writes.
http://www.essaybay.com/

Plagiarism Tools. This gives links to the above sites.
http://www.shambles.net/pages/staff/ptools/