There is an ibook "the art of moving points" by Brian Tindall. It comes with a bunch of videos with further explanations. You can find a few examples here:
http://hippydrome.com/iBookExmpls.html
It also covers modelling and is not application specific.
Not really rigging books, but I always have those on my desk and look things up in them more frequently than in any rigging book I read so far.
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"3D Math Primer for Graphics and Game Development" - Ian Parberry
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"Animal Anatomy for Artists" - Eliot Goldfinger
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"Practical Maya Programming with Python" - Robert Galanakis
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"Classic Human Anatomy" - Valerie Winslow