Matthew Flatt gave a couple of talks at our dept. last week. One of them was on Slideshow, the very cool cross-platform Scheme-based presentation package which most PLT Schemers have been using for conference talks for the past couple of years. Today, emboldened by Matt's tutorial, I used it to give a presentation to my research group, and I'm happy to report that it went off relatively well.
I'm not sure if Slideshow will wean me off PowerPoint for conference talks, but for quick intra-dept. presentations I've mostly been using LaTeX's
slides package; and Scheme's a much better programming language than LaTeX. After hacking around with LaTeX's pathetic
\newcommand macros for so long, it was a huge relief to have real data structures and functions. On the other hand, Slideshow's support for mathematical formulae is much weaker than LaTeX's, although I suppose I could hack up some Scheme code to call out to latex and generate a bitmap (the moral equivalent of George Necula's TeXPoint)...
Anyway, Slideshow's definitely worth a try if you have similar needs. Since Matt may not be visiting you anytime soon, the bundled tutorial on the examples page will get you up and running fairly quickly.
p.s. One thing that's cool if you're giving talks with Scheme code: you can cause the code displayed on your slides to get evaluated at presentation time, eliminating the annoying problem of maintaining internally correct and consistent code examples over many revisions of your presentation --- a problem that invariably bites me unless I proofread each slide about a dozen times (and sometimes even then). This feature is almost cool enough to make me want to hack up an interpreter in Scheme for an S-expression-ized syntax of my own language.