Obviously real estate was the focus of the recent credit (or subprime) crisis. However, many investors believe that student loan debt, which is also bundled and sold (i.e., collateralized), is the next "crisis" area. Student debt has risen substantially, as has the percentage of borrowers in delinquency. See these two articles: Wall Street Journal and New York Times.
Dolvin, Steven D., "Student Loan Debt" (2012). All Chapters. 49.