This fellow, Cliff Atkinson, runs a company called SociableMedia that specializes in marketing and communication around effective use of PowerPoint (no doubt the most maligned communication tool since the stick-in-the-eye.)  Clif has a blog with some VERY useful content.  Subscribed. Here's some of his articles on PowerPoint and effective communication.

Additionally, here are the ToastMaster's Top 10 Tips for Effective Public Speaking and a pointer to my "Scott Hanselman's Tips for a Successful [Technology] Presentation".