I'm very sensitive to caffeine (coffee, pills, energy drinks), but the N.O. Xplode Igniter shots on sport.woot previously worked great for me. I can't say anything about this powdered version, but whatever formula they used in the Igniter Shot gets me going without making me crash, or feel like I'm cracked out of my mind. I only consume half of a bottle at a time though.
I've been trying to up my mass, and the igniter shots have really helped by bringing my reps, weight, and focus up when working out. The L-Arginine makes most people produce nitric oxide, which gives you a great pump too. It also helped me through three, back-to-back hour long classes of Acrobatics, Handstands, and rope climbing. (Though it was still exhausting even on the NO Xplode.) Anyway, I'm sold on the pre-mixed igniter shots, so I'm going to give this a try.