Best. Site. Ever.

[Philondra]

http://www.wolframalpha.com/

This site uses its impressive body of factual knowledge (not opinions) to be able to help you calculate anything that you could possibly ever want to know that can be known using pure facts and systemic knowledge. This can be used for some awesome, serious scientific, mathematical, and factual analysis. It also has some more esoteric uses. For example:

http://www.wolframalpha.com/input/?i=we ... mayonnaise
* This link will give you the nutritional information of Jupiter if we assume that Jupiter is made of 100% mayonnaise.

[Mitra]

Win.

[Karjalan]

Ha thats pretty cool... although now I can't think of anything interesting to ask it.