SlideShare allows you to share a Powerpoint presentation with someone who doesn't have the program, or who would rather not have such a large file emailed to them. Once uploaded (which doesn't require opening an account), you send your recipients a web address, where visitors can flip through the slides in a scaled-down view, or in full screen mode as they would in PowerPoint. Alternatively, you can embed the presentation within your own website.
For new presentations, or the ability to edit online, consider Google Docs Presentation module.
(Macworld) | Cost: | Requires: Powerpoint or compatible software | For further info...