I agree with Paul, Alicia and Tina as well. I believe that the four biggest culprits are the rating agencies, sub-prime mortgage lenders, investment banks and central namks. I believe the central banks is up there because the FED had many ways to prevent this. Greenspan didn't agree to regulate the business spending and banks. He also left the federal funds rate too low which let the house prices rise. This low interest rates may have encouraged many mortgages to be lent out even to the people, who can't handle it. When the federal funds rates rose in 2007 to 6.25%, many people couldn't pay it even the people trying to build their good credit. The FED has alot of explaining to do we'll see what else they have to say today.

Federal Funds rate
This is the rate that banks use to interact with each other overnight.

More information about it: http://useconomy.about.com/od/monetarypolicy/a/fed_funds_rate.htm

Another word I fell across is quanitative easing, just as a summary. It is a government monetary policy placed to create cash flow by buying government securities. This is used to increase the liquidity of the banks. The banks would be able to lend more money and the cycle continues. The bad side to this is that there is a fixed amount of goods for sale, even though there is money in economy and this will lead to the inflation rate increasing. This would then affect other rates and other institutions which may cause disaster.

http://www.investopedia.com/terms/q/quantitative-easing.asp