Slideshare is by far one of the most useful tools I have come across to date. It comes complete with already created resources that are ready for use. No need to reinvent the wheel.
This tool is a fantastic resource to use in a classroom context as it encourages students to take responsibility for their learning and allows them to control what they view and produce depending on their personal learning style. Aligning closely with both Keirsley and Schneiderman's Engagement Theory, students would not only be interested in their learning as they are making the choices about what it is they want to view, they also have the full control of the information they want to include in their work.