Lyriosma ovata (potentwood, marapuama)
This herb, used for centuries in South America to treat sexual dysfunctions, is actually the bark of a tree. As such, it must be decocted (boiled for a while) in order to exctract the beneficial substances.
As far as actual effects go, it appears to be similar to yohimbe
but milder and without yohimbe's side effects. It hasn't been analyzed quite as much as the African plant, and I suspect pharmacological studies in the future will reveal very interesting facts.