I found this really great video that explains the economic meltdown from Jonathan Jarvis (by way of Planet Money Blog at NPR, one of my current favorites for easy to understand info on the economy):

The Crisis of Credit Visualized from Jonathan Jarvis on Vimeo.
I think this is superior to the video Larry Ferlazzo recommended from dot.sub which had what I would regard as an inaccuracy by listing the end of Glass-Stegall as a cause. This one is almost as simple, has better graphics, and is pretty accurate.