The Breathing Earth: Interactive Map Tracks Global Emissions in Real Time
I could play with this Breathing Earth map of CO2 emissions, birth rates, and death rates all day long. (I'm also a huge map dork.) Basically, it simulates in real time the growth (or, occasionally, decline) of national populations and their respective emissions of carbon dioxide. You can hover over individual countries to see their emissions and population data compared to the rest of the world. Or you can just sit and watch as the greenhouse gases rise.
I would suggest, though, that if you do sit and play with it for hours, that you turn the sound off. It's creepy.