Wolfram|Alpha
WolframAlpha.com is kind of like Google but instead of fetching web results it fetches data. I just spent about 20 minutes playing with it and it's pretty incredible.
Here's a link to a screencast demonstrating some of the main features: http://www.wolframalpha.com/screencast/introducingwolframalpha.html
They're in the process of launching, the site is live right now but they're working out the kinks in their cluster/server setup trying to officially launch by Monday. Cool that they're showing behind the scenes like that.
Watch live video from Wolfram|Alpha on Justin.tv


