Glogster
Interactive poster site which enables you to embed images, sound, and video files. Great alternative to poster board for students and a great way to produce study guides for students, too!
Fifty Sneakers
Interactive quiz/test-taking web 2.0 site for many subject areas, SAT prep and Drivers Ed.
Voicethread
Collaborative, interactive video/slideshow discussions by groups. Great way to transform your classroom.