Eric Meyer and gang has released a very useful alternative to Microsoft Powerpoint called S5. It uses XHTML, CSS and Javascript and thus is very usable and accessible. The feature I like most is that it is very printer friendly. Check it out.
S5 is a slide show format based entirely on XHTML, CSS, and JavaScript. With one file, you can run a complete slide show and have a printer-friendly version as well. The markup used for the slides is very simple, highly semantic, and completely accessible. Anyone with even a smidgen of familiarity with HTML or XHTML can look at the markup and figure out how to adapt it to their particular needs. Anyone familiar with CSS can create their own slide show theme. It's totally simple, and it's totally standards-driven.