Married Kama Sutra.

For those of you unfamiliar with the Kama Sutra, it's an ancient Hindu text, much of which describes human sexuality within the context of spiritual enlightenment. The version that we get in the West mostly features depictions of various sexual positions. Here is an example:

Two very funny dudes, Simon Rich and Farley Katz, created The Married Kama Sutra: The World's Least Erotic Sex Manual (Amazon link here). Sad and Useless published a bunch of the images:

See the rest here.