ritalin??? thats the one i tried last year, piece of advice dont get hooked on it other than that it keeps u going for an enitre 24 hour with no drop in concentration but the once the effect wears off u will be shattered and thats an understatement u feel like u've have'nt slept for a week,
http://en.wikipedia.org/wiki/Ritalin
adderall as burke posted is the same thing, it belongs to the same pharmaceutical class.
p.s i recommend u consult a physican or a pharmacist before u go ahead and use it. i dont know how it works in yr country but here its easy tog et it even though its not an over the counter drug over here. but it might be in the us or england so i recommend u ask a specialist who knows the side effects and/or the interactions in case u take other medications like hypertension drugs etc