I tried a bunch of supplements and herbs. Some worked, some had nasty side effects, and most did squat.
The short list is I tried: Piractem, GABA, Rhodila Rosea, Cocamine (chocolate extract), gluractone (red bull ingredient), various ephedrine like stuff, various methly caffeine things (ie green tea), Yohimbine (I highly recommend you never ever take this).
I used to have lab like jars of the stuff at work and my coworkers would call me "the mad scientist".
Nothing worked better than exercise, sleep, nicotine, staying hydrated, and coffee. Strategic fasting is also effective but you have to be careful with that as well (ie intermittent fasting).
The other issue with trying weird stuff is we know a lot (longitudinal study wise) about nicotine. We don't for lots of natural supplements (just my 2 cents). I also can't stress it enough... do not take Yohimbine.. (that stuff should be illegal).
EDIT for Yohimbine explanation (I can't reply to ducttapemaster):
Yohimbine made me extremely lightheaded, extremely anxious, extremely nauseous and I could not sleep for 3 days and I think it was only 5 mg of HCL. I would rather have kidney stones again than go through Yohimbine...
The sick part is I have tried it multiple times (I guess to be scientific about it :) ).