So I gave a public lecture last (Monday) night called, "Afraid of the Dark: How We Know What We Can't See" and videotaped it. Now, I'm pretty good at what I'm doing right now (research in theoretical cosmology), but I'm really good at public speaking and teaching, and here is me telling a public audience all about dark matter, how we know it exists, what makes it different from normal matter, and what I'm trying to do to find it/discover its nature for a good 40 minutes. (The intro and question/answers are cut out).
It was a lot of fun; the audience was wonderful, and actually kept me for more than a half hour after my talk ended, asking questions that they were curious about! The video and audio qualities are not the best, but if you have 40 minutes and a pair of headphones at work, check it out. We've got a (60 Meg) video of the event right here... enjoy!
Alternatively, you can see it in 4 separate youtube parts (below):