I was planning to write this post when Wolfram|Alpha came out, but I didn't get around to it.
Wolfram|Alpha is an audited knowledge base of information that can compute just about anything. I've compiled a list of examples below that don't even show half of the possibilites of Wolfram|Alpha - but are pretty damn cool demos of the power that Wolfram|Alpha gives you.
I think I better stop now, but I really could go on doing that forever.
My absolute pet peeve about this site is the fact that it's called "Wolfram|Alpha". That's just plain ugly. "WolframAlpha" or just "Wolfram Alpha" would look waaaay better. Somehow I don't think that it will get turned into a verb either...
Try it out for yourself, or watch the overview video from which I loosely based my examples.