Kratom and Mescaline are definitely candidates for top 5.
The LSA containing seeds might also make that list. I hear there is a kitchen method for a synthesis by brewing them in wine.....it doesnt make LSD but makes some other analogs I guess. I have never tried it.
I hear there are some kitchen methods for brewing up the oils found in sassafras and sweet flag...I dont believe the result is anything outright banned even....Its a little less interesting and more likely to cause tachycardia and high BP, but its still worth mentioning. A conversion takes place in the liver. We used to use liver samples in test tubes in class.
Khat is legal some places....not here unfortunately.
Betel nut is enjoyed by some people.
Amanitas are definitely interesting and trippy....I hesitate to nominate them for top 5 just because they are hardly enjoyable. They are not exactly euphoric, but they do offer a new perspective
Valarian, Kava, Blue Lotus, Mulungu.....These are all mildy interesting, but nothing mind blowing. Mulungu is pretty useful for anxiety.
The individual ingredients for Ayahuasca are legal most places....One of the most powerful drugs you will ever take. I dont see it as being very addictive or having much potential for abuse though....Its not a pleasure drug and I doubt most people will be chasing that high.
Salvia is worth noting. Its pretty powerful. Like Ayahuasca, its not especially 'fun' but it is a potent tool for altering your consciousness.
Ephedra is still a pretty decent stimulant...Use caution though.