I’ve read, heard and seen many good presentation and article on methodologies in making excellent presentations using PowerPoint or Keynote. I just read this blog post which does a really good job summarizing most of what I’ve heard and adds some insight into common pitfalls and rational in the creation of a presentation.
There is one thing I should add that I heard in a presentation on creating good presentations. Create your presentation with everything you want in it and then replace as much text as possible with a picture, illustration or single words.