Great topic! I would recommend reading the book [i:4b0777b28e]Holy Smoke[/i:4b0777b28e] if you liked the movie. If anything, the book shows the cult aspect better than the movie.
Some more "cult" movies:
Wicker Man (the original)
The Believers (OK, it's a horror movie about santeria, but it kind of qualifies)
Out of curiosity, I did a search on IMDB for "cult"
There are 3 movies called simply [i:4b0777b28e]Cult [/i:4b0777b28e]- there is no detail on the first 2, but the most recent is about a cult, although it sounds like more of a thriller.
Here's a comedy called [i:4b0777b28e]Cult Life:[/i:4b0777b28e]
And a TV movie called "Can Ellen Be Saved?"
Here are some I haven't seen that are fictional:
There was a good one on Jim Jones and Guyana that I saw on cable TV a while ago. I can't find it on IMDB, but I did find this:
] It's a TV movie about the Guyana tragedy.
Here's one about Waco and the Branch Davidians: [i:4b0777b28e]Waco: A New Revelation[/i:4b0777b28e]http://imdb.com/title/tt0259731/
And one about the Mormon polygamists: [i:4b0777b28e]Banking on Heaven[/i:4b0777b28e]
This one's not exactly about a cult, but it exposes the co-opting of Native American spirituality by the New Age movement: White Shamans and Plastic Medicine Men