[iliis]

For more general math there's also WolframAlpha. Eg.: http://www.wolframalpha.com/input/?i=partition+1034

They are also quite capable of blowing my mind sometimes. (Try "When will the ISS be visible?" or "coastline length of africa / length of stride")

[nathanb]

It blew my mind when I wondered how many femtoseconds it had been since the start of the Roman Empire, and it obligingly told me: http://www.wolframalpha.com/input/?i=now+-+founding+of+the+r....

It also told me how many ergs are in a jellybean and what time the sun would set on April 2nd (http://www.wolframalpha.com/input/?i=sunset+april+2nd%2C+201...).

Of the many technologies I use, Wolfram Alpha is the one that feels the most like the future sometimes.