Is Psilocybin The Next Cannabis? covers the benefits of psilocybin and discusses the difficulties of getting it legalized in comparison to cannabis.
Personal comment: Psilocybin is following a legalization track based on relieving existential anxiety in terminal cancer patients. I would be interested to see how psilocybin would perform if substituted for MDMA in the studies on PTSD. I suspect it would do pretty well.