Synephrine. Although I don't know if you can purchase it by itself anywhere? Also I find by adding about 20-25 grams of carbohydrates seems to make it more effective for me as far as the stimulating properties go.....but that sorta defeats your purpose I suppose.
I would buy the prescription strength yohimbine (Its MUCH more potent then the OTC shit) http://www.rejuvenationfoundation.org/ shipping is SLOW about 30 days.