Chrome: Chromey Calculator puts all of the best Google Calculator tricks right at your fingertips, along with a helpful list of your most recent calculations and the ability to turn recent results into variables for trickier calculations.
In addition to the list of recent calculations, which is great for easy reference, Chromey Calculator lets you access the original result in Google. If the Chromey Calculator Enhancer is installed, you can also quickly pop out Chromey Calculator with a hotkey (Alt+C). Knowing that Chromey is saving your recent results, you can use them to fire off new calculations - "@" can be substituted for the most recent result, so you can feed the calculator "@ x 12.167" rather than have to enter in the actual numbers. More maths tricks and keyboard shortcuts are explained at the extension page.
Chromey Calculator is a free download and works wherever Google Chrome works.