Plagiarism can be difficult for most entering college students to understand. They seem not to understand the different ways in which plagiarism can occur. This resource does an excellent job of providing examples that are very clear and detailed. This resource would make an excellent addition to the materials I use when discussing plagiarism with my research writing classes.
If it would not overload the resource, I would add a section on the differences between quoting, summarizing, and paraphrasing.