In October of last year, MIT rounded up five of its researchers to give a panel discussion on the state of the economy, and how it got there. The whole sold-out session is online, courtesy of MIT's TechTV.
I think it may be a bit too jargon-filled for non-economists to absorb in one sitting, but it's at just the right level for 1st and 2nd-year economics undergraduates. Thanks to Michael Picard for the link.
For non-economists, my favourite explanations of the sources of the crisis remain This American Life's two brilliant episodes, The Giant Pool of Money and Another Frightening Show about the Economy. Be warned, though, that the announcer had laryingitis during the first of the episodes.