As far as books go, there aren't any, unfortunately. I think it's because the mortgage-backed securities market is largely confined to professional investors and traders who learn everything on the job. Stocks are the opposite: it's dead easy to open an ETrade account and buy some shares, so there's a ton of information for individual investors.
Lots of people use Fabozzi (http://www.amazon.com/Handbook-Mortgage-Backed-Securities-Fr...) as a reference, but I'm not a fan... it's disorganized, not particularly well written, and doesn't provide much information on how the market works on a day to day basis. The Salomon book (http://www.amazon.com/Salomon-Barney-Mortgage-Backed-Asset-B...) is popular too, but I've never read it.
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