Markdown for slides is a great idea. Don’t painfully lay out each slide, click by click: just write down an outline and let a program generate the slides for you. The almighty Pandoc does this very well. You write plain text, and a single pandoc command produces slides in one of a number of nice HTML formats (like reveal.js or slidy), ready to be uploaded, or in PDF.
I switched over to this way of doing things last year. It was a relief to stop fighting with Keynote,1 which is nice as presentation programs go but still exhausting: it constantly makes wrong guesses about formatting; putting text where you want is a struggle, and inevitably imprecise. And, worst of all, adding notes for myself to slides is pretty hopeless. I always ended up having to create two parallel versions of each class: the slides, and my own notes. That involved a lot of redundant work. By contrast, once I started writing my slides and notes together, I got my materials for class together quite a bit faster. Whether the temptation to further procrastination/tinkering was really healthy is a separate issue.
Anyway, markdown for slides with pandoc is pretty simple and easy-to-use, but because I wanted some features that the HTML formats do not easily support, I was tempted into going with pandoc’s capacity to generate LaTeX slides using the beamer package. Getting what I want out of that setup is what makes easy slides difficult. (If you want easy slides made easy, consider Ben Schmidt’s suggestions.) Here’s what I do these days. All the bits and pieces for doing this can be found in my repository of TeX stuff on github, in the lecture-slides directory. [Edit, May 18, 2016: I now use a slightly tidier set-up, available in a new repository.] For a sample of the kind of results I get, see the slides from my Early Twentieth-Century Fiction course this semester, for example a lecture on Djuna Barnes.