The only real hereditary monarchy today seems to be that of Kim Jong Il. He's an absolute ruler par excellence in the tradition of the Inca. People often speak of the Inca empire, but only one man was the Inca. He owned all property, real and personal. He also owned all of the people. It didn't work too well, however; the Aztecs, who ran an essentially free market economy, had a far more stable society. If they hadn't had the habit of capturing and sacrificing many thousands of their neighbors, they could have been on the way to civilization. Cortez had no trouble organizing the other tribes to make war on them.
Kim is really the only king left who behaves as a king.