For almost seven years now (!), I've been compiling an occasionally-updated list of tips and tricks on giving good presentations and talks—and avoiding bad ones. That takes the form of links to articles and advice from experts around the Web on the topic.
You can always find the list at penmachine.com/powerpoint—but it's not really about Microsoft PowerPoint. In fact, much of my commentary is about avoiding PowerPoint, or at least not giving presentations the way it generally leads you to do them.
A good talk is three things: informative, memorable, and entertaining. I hope the advice I link to can help all three parts of your talks be better. And if you want to see how all three can really come together, watch Dave Olson's WordCamp Vancouver session from earlier this month, "Art and Tech Are Old Pals," or any of his others.