Want a good understanding of the causes of the sub-prime mortgage crisis? I'd recommend this This American Life episode, but it's not free. So, you might like to check out it's companion story, over on NPR. There's also the subprime primer, which is a good, humorous overview, but it doesn't give nearly the depth you get from TAL.
This week, This American Life did a follow-up story, to explain what's happened in the last two weeks. It's very, very good, and available for free download for the next little while. Money mutual funds, the commercial paper market, credit default swaps, netting, leverage, all very nicely explained and explored. Bonus: includes Modest Mouse's Bankrupt on Selling. Get it, and spend an interesting hour.
Edit: The Giant Pool of Money episode isn't available for free download, but it can be streamed for free, directly from the link above. You might even like to listen to it before this week's episode - it gives useful background information.