If I had to recommend one thing, it would be piracetam. Do a bit of reading here on the interbutt about it. Without a doubt, it works, but you have to be pretty good about taking it a few times daily for a while before you'll really be sure it isn't placebo.
The effects are subtle most of the time, but when you're actively using your mind, the enhancement becomes obvious. I recommend between 2.4g and 4.8g a day, though the most effective dose varies between individuals. It works best combined with a choline supplement, like centrophenoxine or alpha-GPC.
Be sure you're getting enough B vitamins; a daily supplement should be fine, along with a good multivitamin.
Also, piracetam makes weed qualitatively much stronger. Take that for what you will.