Horny Goat Weed... does what you expect.
The story goes that a man noticed his goats being particularly randy after eating the leaves of a certain bush.
Although that is its primary use, the truth is this herb does quite a bit more than just that. Known as Yin Yang Huo in China this plant has been used for thousands of years.The recommended dose is 1/2 to 1 teaspoon which is 2-4 grams.