A nootropic, by definition is a drug which will increase learning capacity, and has more recently broadened to mean any 'wonder drug' that may reverse aging, help depression etc. A common example is Phenylalanine - An amino acid that is the precursor of tyrosine which means it will build tyrosine, and hence dopamine which is the main chemical tied in with serotonin. There are also more common nootropics such as vitamin complexes like Ginko Biloba and ginseng. A list of nootropics obtained from lycaeum are:
Adrafinil - stimulant
Deprenyl - memory, learning capacity
Dhea - anti-aging
DMAE - memory, learning
Ginko Biloba - memory
Vasopressin - memory

Most of the nootropics are concerned with memory and learning capacity, but no tests have actually proven that any work.

For further reference, anyone interested in nootropics can read:
Smart drugs and other nutrients by Ward Dean and John Morgenthaler.