I discovered Slide Boom when I was searching for an interactive World War II map (see below). Slide Boom is a website that allows users to upload Powerpoint presentations and the website converts the file to a flash movie. Each presentation that is uploaded can be shared with others on a blog or website. The slides are uploaded in the same manner as the original .ppt file, including audio, animation, and visual files.
My favorite feature of Slide Boom is the animation options such as a pen, highlighter, or eraser. You can save your writing and animation of each slide. You can then make the presentation available to your students. For example: I animated and highlighted the battles on the interactive WWII map. 
Here is a how to use Slide Boom guide.
Here is the main features of Slideboom:
- It has a basic free version and premium version (Basic is fine for educator)
- It is very simple and easy to use
- It allows you to upload PowerPoint presentations and slideshows
- It can be used to convert PowerPoint presentations to Flash
- You can share your presentations with others
- Search for presentations in 100+ different languages and by 30+ categories.
- Join an interest group or create your own
- Embed presentations into your blog or website
