After purchasing too many sub-par reference books on anatomy for artists, I highly recommend the Bridgeman books. This one stresses the hinges and joints of the body and how their bending and twisting movements affect the external shape of a figure. Nobody has studied the figure as long or as intensely as George Bridgeman and it shows in the superb illustrations, many apparantly constructed from memory. For economy of line and accurate sence of under-structure, the illustrations can't be beat. Incidently, "Bridgman's Complete Guide to Drawing From Life" incorperates much of the above book, along with several others, and is a better buy. (It's also a larger format book!)
I also recommend "The Human Figure: An Anatomy for Artists" by David K. Rubins.