I just finished a video giving the background for preference voting. You've come across voting methods if and only if you've taught liberal arts math. It's a fun topic. The video is posted below.
I tried to let go of some of my perfectionist tendencies with this video. There is one place when I say "restaurant" when I mean "office". You can hear the clicks of the keys as I go through the PowerPoint.
The music was provided by Kevin McCloud on his website http://incompetech.com. He has a good selection of royalty free music. Just be sure to give him credit if you use it.