There are many advantages to using LaTeX for your presentations. First, LaTeX presentations require less disk space to store than their PowerPoint or Keynote counterparts. With disks being cheep these days, this is not much of an issue. But, I still like the idea of keeping file sizes down when I can.
Another reason for choosing LaTeX is if your presentation uses lots of mathematical equations.. If you use LaTeX, you can easily copy and paste these into your slides. Otherwise, you need to some way of getting them out of LaTeX and into your presentation software (maybe using tex2im or TeXShop).
Finally there's the simplicity factor. I don't know about you, but the world we live in has become preoccupied with appearance at the expense of content. I find it distracting to go to a talk and watch cute animations and graphics when plan old text would have been a lot clearer. Yes, a picture is worth a thousand words, but the picture does not need to fly on to the screen for the slide to be effective.
With LaTeX, there are many ways to create quality slides. The simplest is to use the LaTeX slides class, which comes with your LaTeX distribution. In the past, if you wanted to create slides you used SLiTeX. Today, this has been replace by the slide class. The slides class enables you to create simple slides with very little work.
There are many other ways to creating slides with LaTeX. Some of the most popular are FoilTeX, Prosper, Seminar, ifmslide, pdfslide, PPower4.
I create my presentations using a combination of PDFLaTeX, FoilTeX, and PPower4. My needs are quite basic, as you will see in the example slides [Insert link to slides.tex]. For a more complete solution, see ``Creating Presentations in PDFLaTeX'' by Matt Welsh (see the Reference sections).