Preezo
Preezo is a site that lets you create online presentations. Just sign up for a free account, and you can create a presentation using an Ajax user interface that will be quite familiar to PowerPoint users. This is especially nice if you are collaborating with others on the presentation, because everyone can use a centralized document. Also, sharing the presentation slides is easier than with PowerPoint.
What a nice alternative to printing out all of your slides for your audience. This way they can just visit a URL to get the slides.
The only alarm bell that goes off in my head is what happens if the Internet connection is down? If I do it on my local drive, I always have access to at least my slides. This way, I may not have anything.