Global Financial Crisis, 2008-2009 - this will find most books related to the 2007-2009 financial crisis and the government's response.
Mortgage Loans - this will find most books on the subprime mortgage loan crisis.
Troubled Asset Relief Program (U.S.) - books & government documents relating to TARP
Financial institutions - Government policy - United States - books & government documents on how the government regulates financial institutions
Please note there are many more subject headings that might be useful when conducting your research on the 2007-2009 financial crisis. These are intended to help you get started.