Prezi is similar to PPT, but it's interactive. You can have several people collaborate on it. It's non-linear and is not in slide format, but rather in a big canvas and you control where the focus goes. The zoom and pan out feature is really cool as well.
Jing, together with Camtasia Studio and Screencast are an amazing product. You record with Jing, save it into an MP4 with Camtasia and publish it to others with Screencast. These are by far my favorite tools, but I have never used them with students. WIth jing you can share your screen and talk over what you are seeing on the screen. Camtasia gives you the ability to edit what you created, add in call outs, zoom and pan, pixilate images, use tools like circles, arrows, dialog bubbles, etc. and then publish them with a URL to share with others. I would love to use this tool with students.
VoiceThread allows you to upload different media to create a project and then share it with others. Those that you share it with can collaborate with you on it by communicating through a type of discussion board.