I use google’s built in search features a lot, especially for converting units such as mm to inches, Fahrenheit to Celsius and so on. You just type the query directly into the search field and voila.
Recently Google has added some new functionality with graphs. Searching a mathematical function such as sin(t) will show you a graph of that function, which you can zoom horizontally and vertically. It’s another nifty feature, useful for getting a quick visual of a function.