Nootropics is a relatively "new" science of determining which drugs and nutraceuticals are beneficial to brain functioning.  This science is also known as the science of "smart drugs".  There are many classes of smart drugs, but they all perform essentially the same function, to enable the recipient to perform greater mental tasks.  The mechanism of action varies and like most drugs is usually unknown.  The experiments are usually performed on rats or other animals and then performed on human trials.  Below are some links to various nutrients that help with brain function.

Aniracetam

Centrophenoxine

Piracetam

DMAE

Acetyl L-carnitine

Vinpocetine

Lecithin - and associated phosphatidyl groups

So where does one get this stuff?  I am a member of the Life Extension Foundation and I find them to be a great source of information  you can reach them at www.lef.org