The "Daring Librarian" has put together a number of posters using ComicLife to explain a number of Web 2.0 web-based applications and resources
These posters are available in a variety of sizes and are great for printing and putting up in the staffroom or the library or computer lab.
Complete Set:
How to Use KeepVid to save Youtube videos
Customizing a Blogger page
Wikipedia at a glance