I have been griping for a long time about how nutrition labels should include the number of mg of caffeine per serving in a drink (or food). I'm not sure if that will happen in the future or not, but in the meantime there is this really interesting website, with a database of the caffeine content of most of the common sodas/energy drinks/coffees on the market.
Just as a baseline, coffee has about 107 (brewed) to 145 (drip) mg per cup. I was surprised to see that many energy drinks actually have less caffeine than a cup of coffee, although some have disturbingly high counts: the 'winners' are Boo-Koo Energy, and Zero Carb Rockstar, each with 360 mg.
I also thought it was interesting that the Zero Carb version of Rockstar has more than twice the caffeine of the regular version, which has just 150 mg. Hmmm.
Anyway, another cool feature on the site is a little gadget that tells you how much of an item you would have to consume to get a lethal dose of caffeine. Just for the record, it would take 19 cans of Zero Carb Rockstar to kill me, but I could drink 47 cups of brewed coffee before kicking the proverbial bucket. Rock on.