Here's a pie chart that puts into perspective the size of the Fed's involvement in the financial crisis. The entire circle represents approximately 8 trillion dollars. Yes, $8,000,000,000,000. The blue quadrant represents federal lending including expansion of swap lines to the tune of about $2 trillion. The purple quadrant comprises housing related purchases ($1.45 trillion) and buying $1.8 trillion of commercial paper. You can see a more itemized breakdown here.
The graph was put together by the Atlantic's Timothy Lavin and Anup Kaphle.