I got a free sample bottle of this at the Maker Faire last month. Boy! I've never had a jolt like this (that was legal). It probably differs for everyone, but it works for me. In fact I had a bottle of it + a latte one afternoon in NYC and couldn't sleep at all that night.
Ingredients: Vitamin B6, Vitamin B12, (mega-amounts of the latter two vitamins); Niacin (Vitamin B3); Folic Acid (Vitamin B9)
Citicoline; Tyrosine; Phenylalanine; Taurine; Malic Acid; Glucuronolactone; Caffeine (oh yeah!)
It costs $3.50 a bottle in stores, but is considerably cheaper at Costco or via Amazon.
Caveat: I haven't used it enough to know if it's OK in the long run. And my long experience with boosters, enhancers, and ahem, drugs, is that there's no such thing as a free lunch.