Well the best ones are the 3D models used on National Geographic TV. Those are way better than a flat drawing in a book. You can find one of those flat drawings on the "Science - How Stuff Works" webpage: http://science.howstuffworks.com/snake4.htm
Be advised that there's many, many misconceptions and much misinformation out there on this topic (especially on the web, which is notorious for bad information). Your best bet would be to pick up a textbook on herpetology.
Also, be sure to check out the "Snake Basics" section of the site I mentioned, because they have an anatomy drawing of a snake's inner workings - and I know how much you like those things.
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