Drenamin

The best single supplement I know of is Drenamin made by Standard Process (noted for the quality and efficacy of their products).  Not the easiest supplement to find as Standard Process is quite picky about who they allow to sell their products (normally health care professionals).  One source is CureZone sponsor Utopia Silver.

You might also want to check out this article:

The Reason You are Sick and Tired May be Fatigued Adrenals

Also, supplementary DHEA may boost your libido.