Enhancing effect on some cognitive function, especially in people with brain disfunction. Some studies have indicated that pyroglutamate may help improve cognition in aging alcoholics. Effect may seem to diminish with daily use. A B-complex nutrient that is used,like choline, to manufacture acetylcholine in the body. Also somewhat useful in alcohol recovery.
Many vitamins enhance or inhibit various metabolic pathways, sometimes with nootropic effect.
Read up on toxicity before overdosing onesself with vitamins, though. Although it's useful to promote sleep, I have not seen any evidence that melatonin has any nootropic properties. Ephedra can be dangerous if combined with some drugs, and it isn't a clear-headed stimulant. It's primary use should be as a decongestant.