Google Calculator

Anything that helps with math-related stuff gets a vote in my book. Not only can you use Google to solve simple math problems, you can also use it to convert measurements. Here are a few examples of this; you can simply type these right into the Google search box:

5*9+(sqrt 10)^3=

10.5 cm in inches

sqrt(8912)

And so on. Google can also do much more complex problems and conversions; you can find out how to build your queries so Google knows what to do with them at the official Google Calculator help page.