Talking about the elephant...

Krugman, again, provides sane and measured advice. Here is what I think is key (see previous posts):

What we're going to have to do, clearly, is relearn the lessons our grandfathers were taught by the Great Depression. I won't try to lay out the details of a new regulatory regime, but the basic principle should be clear: anything that has to be rescued during a financial crisis, because it plays an essential role in the financial mechanism, should be regulated when there isn't a crisis so that it doesn't take excessive risks.

(my emphasis)

Succeed in doing this and you can greatly mitigate the public cost of the crisis. The problem is that regulating the companies that are big (and too big to fail) during prosperous times is difficult politically. It goes to the heart of the small government versus big government debate. Republicans would take chainsaws to the regulations, and democrats have a hard time winning elections on a platform of more regulation, particularly as the memory of the previous bubble fades.