Also check out the MagicPoint Presentation tool. MagicPoint takes a very different approach to the problem of editing presentations. This tool is based on plain text files and a custom markup language. Editing of slides is done with an ordinary text editor; the resulting file must be fed to the utility to see the final result.
Check it out:
http://member.wide.ad.jp/wg/mgp/Magicpoint has a few other neat features as well.
1.) Scribbling on slides during presentation with the mouse (two colors)
2.) One pixel time thermometer, visible to speaker, generally not on overhead projector: green for lots of time, yellow for wrap-up, red for time's up
3.) "swallow" features allows one to run an external program (X11) within a slide!
4.) %filter allows one to filter text in a slide through a rendering engine (such as latex2eps) to generate images which can then be displayed within slides.
5.) A variety of pauses, "cut-ins" (text sliding in from one side or another), fades (slide transitions) are supported. There aren't many of them, and they should be used sparingly, but they're simple and functional.