In our continuing effort to keep the viewing experience at Hulu.com as efficient and elegant as possible, we recently updated our site player layout. As such, some features like Auto Play aren't in the same place as they were before. The good news is that the Auto Play feature is still available. At the end of every video you watch on Hulu.com, there will be a popup that says Pause Auto Play. If you click this, Auto Play will be turned off for that video.
If you would like to turn Auto Play off entirely, navigate to your account settings page and un-check the "Turn On Auto Play" box at the bottom.