Does a small Frappuccino give you enough caffeine to be worth the calories? How long would you have to run to work off an iced latte? David McCandless' beautiful chart puts all your caffeine concerns in perspective.
McCandless' chart, posted at his Information is Beautiful blog, puts caffeine on an X axis and calories on the Y, plotting the majority of drinks one can brew at home or shell out spare cash for all around the grid with representative sizes. That allows you to find your personal energy beverage sweet spot—say, 150 calories and lots of caffeine, or almost no calories and just a soda's worth of the temporary boost—and also see the caloric equivalent in food, alcohol, or 30 minutes of exercise.
It looks great, tells a lot of information in a small space, and makes me want at least an A4 print of it to keep nearby for moments of dietary weakness at around 3pm.