The most interesting website! It will do all your math problems for you (including calculus), but that's not all! It handles everything in natural language and for a variety of topics, and it includes visualizations!
You can even type in "hamburger" and it will give you the nutrition facts for a typical hamburger with statistical deviations.
It started with trying to find out when I would turn 10,000 days old (Sunday, January 23, 2011). Give it a gander! Watch this video to see the broad scope of it's capabilities.