Death by PowerPoint

Show http://www.slideshare.net/thecroaker/death-by-powerpoint
Ok, not original but still hard to beat for it's power for making students think about presentations, their construction, purpose and how to make them effective

You Suck at PowerPoint

Show http://www.slideshare.net/jessedee/you-suck-at-powerpoint
Another classic on issues with presentations and PowerPoint

Presentation Bingo

Using key terminology for presentation work.