Hi Henrietta
I have used piracetam -
http://en.wikipedia.org/wiki/Piracetam. There seems to be quite a lot of clinical evidence for it's efficacy at treating a variety of neurological conditions, but it's effects are unstudied in healthy people.
It's available on prescription in the UK but is other unscheduled so it's legal to import from other countries. It is generally regarded as safe and is not neurotoxic, though it can cause headaches.
You should take a choline supplement too (it's a type of amino acid) and is vital in brain chemistry, but cannot be synthesised or stored by the body.
I will be honest, I did not notice any improvement in memory, however I was spectacularly bad at taking it and only managed to last four weeks. A friend swears by it.
Apparently you should play with doses of both piracetam and choline to get the best effect.