My personal Favorite supple of all time and;
Curcumin as it is getting a lot of attention lately. After some googling I'm finding conflicting results, even the exact opposite. eg. "80mg of a bioavailability enhanced curcumin supplement has been reported to increase nitric oxide in serum by 40% or so, which is significantly larger than many other dietary supplements. "They also had decreased levels of free radicals in their blood vessels, specifically superoxide anion, a compound that deactivates nitric oxide (5)."
Few other:
Grape seed extract (GSE) is simply an extract derived from grape seeds.
The extract itself is great for testosterone production, as it’s one of the few natural substances that can block the conversion from testosterone into estrogen. In other words, GSE is a potent aromatase enzyme blocker (more about that here).
But on top of that, grape seed extract is also great at increasing nitric oxide levels…
…Studies on humans show that it drops blood pressure and heart rate, and animal studies show that it activates the natural nitric oxide synthase of the body and increases NO levels by 138% when taken at doses of 100mg/kg (study, study, study, study, study, study).
Icariin is a flavonoid that can be found in a herb by the name of horny goat weed(epimedium).
The herb itself is known for its aprhodisiac benefits, and animal research suggests that it can boost testosterone levels quite significantly (more here).
The active compound in the plant (icariin) is great for nitric oxide production, and it also acts as a mild PDE-5 enzyme inhibitor. Meaning that it works similarly as ED drugs (study,study, study, study) So in a way you could say that icariin is natural viagra with circulation enhancing, nitric oxide boosting, and testosterone boosting benefits.