After doing some school work, I was browsing through a dutch website about math (www.wiskundemeisjes.nl), and in one of the comments linked a site called Wolfram|Alpha... This is the best search engine EVER.
Or, not so much a search engine.. It's a knowledge engine. It can solve almost all your math problems, you can ask it how many days seconds years have passed since your birthday.. Who was born on that day... Or check how much 5 mol of silver nitrate is!
Just check it out:
Popularity: 15% [?]