Tribulus (Tribulus terrestris) has been found to help inhibit COX-2[1], prevent urinary stones[2], and enhance erectile function in laboratory animals.[3]* It has been used in ayurvedic and Chinese medicine for centuries.

References

1 Hong CH, Hur SK, Oh OJ, Kim SS, Nam KA, Lee SK, Evaluation of natural products on inhibition of inducible cyclooxygenase (COX-2) and nitric oxide synthase (iNOS) in cultured mouse macrophage cells. J Ethnopharmacol. 2002 Nov;83(1-2):153-9.
2 Anand R, Patnaik GK, Kulshreshtha DK, Dhawan BN, Activity of certain fractions of Tribulus terrestris fruits against experimentally induced urolithiasis in rats. Indian J Exp Biol. 1994 Aug;32(8):548-52.
3 Adaikan PG, Gauthaman K, Prasad RN, Ng SC. Proerectile pharmacological effects of Tribulus terrestris extract on the rabbit corpus cavernosum. Ann Acad Med Singapore. 2000 Jan;29(1):22-6.