Five years ago it was the dot-com bubble that burst.
Now it's the housing market.
My prediction is the next big thing (since ultimately nobody will learn from the lessons of today and we're a country just dying to invest in something) will be small-business loans. Someone will get the idea in their head that while lending to home borrowers with the hope of the property value increasing was a bad idea, lending to people who want to start up businesses with the stated goal of making money will be a much better idea. And while the intent will be noble at first, particularly in an economy coming out of a recession and people looking for new job creation, it will become so perverted by special interests that eventually lenders will find themselves giving money to unqualified people with hair-brained business schemes that don't have a chance of turning a profit, much less paying back the money.
Of course, money will have to become available to lend, first, but once that happens, I see us starting our way down this path yet again. This is just my guess at how we'll get there.