I'm a big fan of the omega-3's, and I take caps to get a combined 3 grams of EPA and DHA daily. There is little doubt left that these aid cognition and mood, along with a host of other physiological systems.
I also hit the nootropics, using a stack similar to that already mentioned on this thread.
Finally, if I'm tired or need a boost, 3 grams of l-tyrosine really hits the spot. I usually hit this stuff before a heavy session of wrestling, BJJ, or kickboxing.
Speaking of which, I know it has already been mentioned, but strenuous exercise really helps me out. To me, there's no better way to erase a bad day of trading than with the catharsis of physical exhaustion followed by good sleep.