Yohimbe

Pausinystalia yohimbe
This is probably the herb with the second most well-known reputation for aphrodisiac effects, the first being ginseng. One of the more important distinctions between the two is that yohimbe works.
The bark of the yohimbehe tree (of West Africa) has substances that dilate small arteries by blocking the release of neurotransmitters that would otherwise cause the arteries to constrict. This effect is referred to as alpha-2-adrenergenic receptor blocking. So what does that all mean? Well, it increases blood flow to the penis/clitoris and reduces the flow from it. Very erect, very sensitive. Hence, very popular. Some people also report mild hallucinogenic effects.
There's a catch, of course. Prolonged use can bring on side effects such as palpitations, tension, irritability, and sweating. It's very dangerous for people who have problems with their heart, liver, blood pressure, or who are taking MAO inhibitors. If you don't have any of these problems, you should be alright with yohimbe use, so long as it isn't daily or too frequent.