the use of hallucinogens has been allowed since the earlier 90s for a very small community of scientists for the very purpose of working on what was done with them in the 60s.
Brazil has legalized Ayahuasca(DMT) (bad spelling but its close) as a Religious use and churches have spread all over into the US and Europe, look into Santo Daime churches for them up here in the states.
as already said Salvia Divinorum is legal but for how much longer is a good question seeing as how lots of people are toting it as a "legal marijuana" which if youve done it, is so far from the truth youd kick the people who advertise that in the nuts if you ever saw them.
Marijuana is barely a misdemeanor in most places now and Alaska even went as far as to try and legalize in the last couple years, but it didnt pas.
Peyote is legal for the native americans down south, Seeing as how its a indangered plant and takes 20+ years to mature i feel it should stay illegal to pick as numbers of it dwindle and much easier to get and legal cacti are a pretty close experience (Peruvianus/San Pedro)
this was a pretty fragmented post i made, sorry ill fix it later
edit i forgot to add, to answer some more questions i would highly recommend looking into [MAPS
aka Multidisciplinary Association for Psychedelic Studies