What Should be Cited?

You Quote It, You Not It! Tutorial for students on citing sources: http://library.acadiau.ca/tutorials/plagiarism/

Students should be taught from an early age to credit others for their words and ideas.
All media must be cited: pictures, music, videos, etc.
This includes any original material or ideas.
Common knowledge does not have to be cited; facts that would not be known by a student should be cited.
Personal opinion does not have to be cited
Paraphrasing or changing a few words does not make the work someone's own.
Creative Commons has a variety of licencing that may still require citation.

How to Tell if Students are Plagiarizing?

If the student's language is just a little too sophisticated, pick out a phrase and put it in a search engine to see if you get any hits. It's best to put the phrase inside quotation marks. Also search within Google Scholar.
Use TurnitIn.
Ask students to submit their work electronically. Check to see if they have used "web formatting" or their work is in tables, or if there are hyperlinks.
The Platiarism Checker: http://www.dustball.com/cs/plagiarism.checker/ - copy and paste phrases into this search engine. It will suggest sites from where work may have been copied. A similar tool is offered at http://www.plagiarismchecker.com/ .
For documents between 20 and 100,000 words or web pages less than 888 words, try http://www.doccop.com. Note that you much register and accept their terms.
Paper Rater offers a grammar and spelling checker that will also let you know if it feels there's a chance that you have plagiarized from another source.

The Owl at Purdue: Avoiding Plagiarism
Ted Frick http://www.indiana.edu/~tedfrick/plag... - has a good quiz to test your knowledge of this issue
MLA (Modern Language Association): www.dianahacker.com/resdoc/p04_c08_o.html.
APA (American Psychological Association) Online tutorial on the basics of APA style is provided by the American Psychological Association at www.apastyle.org/. Click on the link to "Basics" under "Most Popular".
CMS (Chicago Manual of Style) - University of Chicago Press information by Kate Turabian at www.press.uchicago.edu/books/turabian/turabian_citationguide.html

Evaluate web sources with Credible Sources Count! - http://library.acadiau.ca/tutorials/webevaluation/
Search the web better with - Searching With Success! - http://library.acadiau.ca/tutorials/websearching/
Learn the research process with Research it Right! - http://library.acadiau.ca/tutorials/research/