I'm huge on this stuff. L-tyrosine, at 3 grams, 1 hour after a meal will give you a nice mental boost and is great for pre workout. It makes all your other stims, fat burners more effective. I use this stuff every day, up to 2 doses. the third dose never works as well, so limit this one to 2 doses.
DMAE is a good one as well and super cheap to buy in powder. Stacks very well with l-tyrosine.
Aniracetam with oxyracetam can really help you study. Starting doses are 200mg of each up to 1 gram.
Vinpocetine, increases blood flow to the brain, gives nice focus as well.
I have used all of these and encourage others to experiment with them as well.