One thing I discovered during the latest RIN workshop (thanks to Anita de Waard) was Slidy.
Slidy is a very handy way to create Slide Shows in XHTML and is, in my opinion, much more powerful than PowerPoint or even OpenOffice equivalent. I suggest you to see the Slidy presentation to see the result AND to learn how to use it (it REALLY is simple).
I also suggest you this presentation “Web of Applications” that contains further features available in Slidy.
Now make your slide shows very easily and present them on the web or on any browser. Have fun !