Here are a couple of SlideShare presentations from Sacha Chua that I've featured in the past. But as it has been two years since I last wrote about them and it's the beginning of a new school year, I thought it would be appropriate to highlight them again.
A Teacher's Guide to Web 2.0 at School.
The Gen Y Guide to Web 2.0 at Work.
Both of these presentations are suitable for introducing colleagues and students to the key concepts of Web 2.0 and social media. The Teacher's Guide does a good job of addressing the "yeah buts" that you might encounter from colleagues or administrators who are leery of Web 2.0 and social media.