Some great advice from the Butler University Libraries on how to avoid plagiarism:
Plagiarism.org, is a free resource sponsored by iParadigms LLC, makers of Turnitin, WriteCheck, and iThenticate. Much useful information about what plagiarism is and how to prevent it can be found here.
Colby, Bates, and Bowdoin (CBB) Plagiarism Resource Site's Self Test about plagiarism is a excellent way to learn more about the subject. It is a brief online quiz and can be found here.