Being a savvy citizen of the web, you probably already knew this but…
Google’s search field is an awesome and highly practical calculator. I use it on a regular basis for quick calculations, often when I’ve copied large numbers from some other application.
I particularly like how well Google handles commas, which for some reason seem to stump many other calculators.1 It also handles parentheses, exponentiation, and pretty much any other mathematical operator you throw at it. Unit conversions are no problem either.
Power user tip: Since each calculation generates a new web page, your web browser’s history turns into a calculation ticker tape. Chrome’s HTML history page is especially good at this. Very useful for jumping back to prior steps.
Like Spotlight, for example. LaunchBar’s calculator, on the other hand, handles commas pretty well. ↩