A few weeks back, we looked at Gliffy, an online presentation program that's an excellent alternative to MS Powerpoint for a quick presentation. Now, more advanced users that want to create a professional quality presentation also have an online alternative.
Empressr doesn't hold back a thing in their free tool, making it one of the more impressive AJAX programs I've seen online. While I've just started to play around with the program, I've found it very easy to create basic Powerpoint slides and to also add some multimedia - which can be a bit trickier to master with Microsoft. Since Empressr is entirely web-based, users won't have to worry about problems of launching the slides on a different computer (fonts not working, video not launching, etc). Best of all, the presentations don't have the Powerpoint "feel" which can get a bit tiresome.