I was badly poisoned by ergot a year ago. It isn't really a hallucinogen as much as it is a neurological toxin. It was a horrible experience where I acted irrationally and almost completely lost the ability to form long term memories for about 5 days. The amount that I ate was about equal to one grain of rye in the package I bought from Mother's market. That is more incapacitating than you might imagine. It just made me incredibly stupid.
There is some evidence they may have used peyote.
http://books.google.com/books?id=MVfZ3ZC…
They also used Nicotiana rustica which is a wild tobacco with hallucinogenic compounds in addition to nicotine. They also used the poison gland of the cane toads.
"In fact, the Bufo toad was held in extremely high esteem by the Mayans, and the hallucinogenic substance that the toad excreted was often blended to make the magical potions that facilitated communication with the supernatural. Like many Mesoamerican peoples, a fermented drink called “Balche” was made from the Balche tree (Lonchocarpus longistylus) and honey and was one of the core potions used for divination purposes. The secretions of the Bufo toad were added to this blend, it was consumed with cigars made of the Nicotiana rustica, or evidence, although less concrete, suggests that Blue Lily and/or Morning Glory was added to the brew for one purpose: to open a gateway to communication with the supernatural."
http://www.cleversley.com/myblog/?p=134