LaTeX + Beamer (for typesetting the presentation in a visually pleasant, clean, simple and consistent way) + KeyJNote (for presenting it stylishly to the audience) = a recipe for success. In particular, KeyJNote, which I found only yesterday, seems to be a fine and tremendously useful piece of software, despite being very young. The only annoyance I have found in it is that it doesn’t respond to Alt-Tab when in fullscreen mode. On the typographical side, I used the progressbar Beamer theme and the Torunian Antiqua font, both to great effect.
While I’m at this topic, Jan Rychter has recently posted a great guide to giving presentations, especially short ones. I heartily recommend it to those of you who speak Polish (is there actually any non-Polish-speaking person reading this?)
Update 2010-Jan-17: KeyJNote is now called Impressive.