Keynesianism has dominated modern economic theory for a while now. There are alternative economic theories but they're often ignored. I'd just like to quickly point out the accuracy with which a few economists did, or did not, predict the recession.
You may not want to watch each video through it's entirety because taken together they're pretty lengthy.
First, here is a compilation of videos of Peter Schiff, President of Euro Pacific Capital and former economic adviser for Ron Paul during the 08 campaign. All the videos are taken from 2006-2007:
http://www.youtube.com/watch?v=2I0QN-FYkpw
Next is a video from MSNBC's Morning Joe program in which Ron Paul is interviewed. The relevant portion starts at 1:33:
http://www.youtube.com/watch?v=MQ3JNcMDWwg
Last is another compilation of videos from 2005-2007. This one is of the man currently with authority over our economy, Ben Bernanke who is Chairman of the Federal Reserve:
http://www.youtube.com/watch?v=INmqvibv4UU
Taken together these serve as pretty strong evidence in favor of the Austrian School of Economics and sound money. One correct prediction doesn't instantly validate the theory, but it's also worth noting that the theory's founder, Ludwig von Mises, is often thought to have predicted the Great Depression.