Here’s a interesting Doc Searl’s article on how to make powerpoints an effective tool for communication.
Main points are:

1. Begin with an end
2. Come from who you are
3. Tell your Story : It should comprise character, problem and movement
4.Write from an outline
5. Talk from headlines and not from headings
6. Use graphics
7. Use numbers to make lists memorable
8. Research thoroughly and give examples
9.Make comparisons
10. Stand and Deliver