unDraw - Open source illustrations for any idea
Image library that you can easily customize. These characters might work in some scenarios, but they don't have facial expressions. Available in SVG and PNG.
Students in David Wiley's Project Management class remixed a textbook with an open license to customize it for instructional designers. They added new examples, photos, video interviews, and assessments. See the blog post for information on the project: http://opencontent.org/blog/archives/2119
Moved to http://pm4id.org/