Jason van Cassell is doing an in-service for social studies teachers tomorrow on how to use Prezi. Prezis are a cool alternative to PowerPoints. I like them best as they force the creator to think about a more enticing PowerPoint that can add items such as video, documents, pdfs, pictures and do some interesting maneuvers. Above is a short introductory tutorial and here are others to do more advanced things such as importing from a PowerPoint and creating a Prezi collaboratively.
Here is Jason's how-to e-sheet on creating a Prezi. Here is one on how to upload a PowerPoint into it and finally here is how to register for a Prezi.