Vitamin C, it does wonders.
I'm up at 4 am during the week in order to be awake and ready for work at 5:30. In an issue of InStyle, a fashion stylist said that when she needs a quick boost, she would pop an Emergen-C packet with 2 oz of water and the 1000 mg of Vitamin C immediately perked her up. I now keep one of those packets in my work bag and pop a 1000 mg supplement of Vitmanin C every morning. It does wonders for my energy level.