I'm a medical school professor, so I give and sit through many lectures. Despite 20 years of trying I still can't get them right, but I'm trying. These three sites might help you with your presentations - they've helped me.
Presentation Zen is my latest favorite. Less is more. Make sure to visit the popular posts and presentaiton tips on the links bar.
Guy Kawasaki describes his 10/20/30 rule, which I've never been able to achieve. While he makes reference to venture capital pitches, the rule is applicable to nearly any stand and deliver presentation, especially if you're projecting something. I had a chance to meet Guy at a Lexington, KY computer show back in the 1990's (pre-internet.) I'll never forget that he used a slide carousel and not a computer LCD projector. At the beginning of his talk he noted that he didn't trust computers with something so important, that he was suspicious of slides too (he had overhead transparancies just in case), and that he'd be just as happy giving his presentation with no visuals at all. In that brief encounter he gave me permission to hate technology for it's shortcomings while still loving it for it's promise.
Lastly is Ian Parker's Absolute Powerpoint piece in the May 28, 2001 New Yorker (I link to a web based text version) that should be required reading for all powerpoint users.