I thought the demo for Admob was extremely compelling and executed perfectly. If you only have time to check out one of the great videos on there then go for that one: http://www.youtube.com/watch?v=w7E5PosTG2U
What was really successful about his pitch though was his tone. He is VERY believable. He comes off as so true. Add to that the fact that he told us that we was only going to cover three things and then nailed them, and man, that's a nice pitch.