There are various species of psychedelic cacti; the common active constituent is Mescaline, though other alkaloids are reported to be present in differing species.

My personal experience with cacti is limited.  I have not ingested, but I did get some seeds from Gnostic Garden (no longer trading).  I bought some Peyote and some 'Peruvian Torch'.  They took months to germinate.  I almost gave up on them.  Out of about 20 planted Peyote seeds I got one cactus.  Out of about 60 planted 'Peruvian Torch' seeds I got four cacti.

It should be noted that my germination procedures were a bit rough and ready, consisting basically of sticking the seeds in a pot and trusting to luck.  I did use cactus compost, and for some of them I did microwave the soil to sterilise it before planting the seeds.  I could see that the sterilised pots definitely had less subsequent growth of moss on the soil surface.  There are doubtless more steps that could be taken that would probably ensure a better success rate.  A good web-site is Ethnobotany Lophophora>>

My seeds germinated at the end of summer 2000.  The peyote did not survive the first winter (even though all cacti were sown and grown indoors).  The Peruvian Torch did survive, though growing hardly at all. - Tiny things, the size of my little fingernail!  Subsequent summers have seen an acceleration in growth rates, the biggest reaching10-15cm in height by the end of the second year.

There follows some brief notes on some of the species:

Peyote (Lophophora williamsii) aka: Peyolt
The most frequently heard of species, which has become known through its traditional use by native Mexican/American cultures.  Peyote was one of the principle psychoactive plants given to Carlos Castaneda>, referred to particularly in his earlier books in his accounts of teachings of don Juan. More recently (and after some 'to-ing and fro-ing') it has been granted some legal recognition in the US with regard to its use by practitioners of the 'Native American Church'.

Due to increasing demands Peyote is becoming rarer in the wild.  It can be cultivated, but it grows quite slowly, and after investigating alternatives many people grow other species of psychedelic cacti.

San Pedro (Trichocereus pachanoi) aka: Aguacolla, Achuma, Huachuma, Gigantón
This faster growing columnar cactus is a popular alternative to Peyote. It has been traditionally employed by shamans in the diagnosis and curing of illness since around 1300 BC in the Andes of Peru, Ecuador and Bolivia.  

Peruvian Torch (Trichocereus peruvianus)
Similar to San Pedro (T. pachanoi) but with longer brown spines, this species is often preferred San Pedro as being more potent and even faster growing. It can reach a height of well over 2 meters can withstand temperatures as low as -4°c.