L-Citrulline is one of the most effective nitric oxide boosters found in many pre-workout formulas. Not only does L-Citrulline help produce massive pumps, but studies have also found L-Citrulline to have potential performance benefits as well. Shoot for 3-6 grams 30-minutes before your workout.
Reference: Willoughby, D. S., Hwang, P., & Willoughby, D. S. (2015). Intracellular Mechanistic Role of Nitric Oxide: A Comparative Analysis of the Effectiveness of L-Arginine and L-Citrulline Supplementation on Nitric Oxide Synthesis and Subsequent Exercise Performance in Humans. International Journal of Food and Nutritional Science, 2(1), 0-0.