The Writing Center is continuously working on this "resource bank" for faculty and would love to hear any suggestions of resources you'd like to see us add.
This survey from turnitin.com provides a lot of insight into how instructors across the country categorize types of plagiarism, and includes their ratings of the seriousness of each type. The examples provided could serve as a lesson on the topic for your students. Online version: Plagiarism Spectrum. Downloadable file (requires registration): Plagiarism Spectrum.