Jeff Jarvis says he's found it.
UPDATE: He's right. Ira Glass and company did a terrifically excellent job.
They give easy-to-understand explanations of mortgage-backed-securities, commercial paper, tranches, credit-default swaps, and an alternative to the Paulson bailout plan called "stock injection". Apparently this bailout variation is preferred by a majority of professional economists.
Jeff also points to a site that tries to pull together the best thinking about the mortgage/credit/stockmarket crisis. It's called TheMoneyMeltdown.com.
UPDATE: The folks who did the explaining for Ira Glass now have a website with daily podcasts called Planet Money.