http://owl.english.purdue.edu/owl/resource/589/01/
This resource offers advice on how to avoid plagiarism in your work, including exercises and information for teachers.

http://writingcenter.gmu.edu/resources-template.php?id=1
A brief overview of what plagiarism is and how to avoid it.

http://humanistic.mit.edu/wcc/avoidingplagiarism
The best way to avoid plagiarism is to understand what it is.  Then take steps to avoid committing either accidental or intentional plagiarism.  This is a guide that discusses three other terms that need to be defined before plagiarism is addressed --quotation, paraphrase, and summary.

http://writing.colostate.edu/guides/researchsources/understandingplagiarism/index.cfm
A guide that helps clear up any questions you may have regarding plagiarism.