One of the famous natural boosters is Animal Stack. It contains herbal ingredients such as Longjack, Tribulus, etc. to help boost testosterone. However, people feel that most of the ingredients in Animal Stack play no role at all as testosterone boosters. Experts believe that the manufacturers add extra stuff to make it more attractive, apart from the usual testosterone boosting ingredient, Tribulus. A certain number of people feel that it is one of the best testosterone boosters.