Omega-3 Epa/Dha supplement. It's the same stuff as in fish oil, but you can also get a non-fish version (for veg*ns, or just those not interested in possible contaminants in fish) made from algae (where fish get THEIR omega-3's from!).
I just picked up this brand--http://store.nexternal.com/shared/StoreFront/default.asp?CS=vegane&StoreType=BtoC&Count1=608913600&Count2=526054024&Keyword=EPA&Target=products%2Easp&Submit1.x=12&Submit1.y=10 -- and really like it.
No 'fishy' taste or aftertaste (I've tried algae-based omega 3's before and they gave me 'fish burps': I guess fish must get their fishy taste from algae as well?), easy to swallow, high quality.
Mint is an aromatherapeutic fix for memory and concentration. Just take some natural-flavored (not artificially flavored) mints or gum, or buy a bottle of mint essential oil and sniff it (I've also seen small 'sniffers'? that contain mixes of essential oils like mint that are supposed to boost concentration.
As someone else mentioned, ginko biloba is supposed to help with memory (by increasing blood flow and subsequently oxygenation).