One of the Google Search features I use fairly often is the Unit Conversion feature. It supports a number of different conversions including temperature, distance, weight, and many others. For most simple conversions, it saves you the trouble of searching for a tool on another website.

Generally, I've always opened Google in a browser, typed in my units to convert, and hit the Search button. Recently, I started typing units to convert in my Google Toolbar, which I usually only use for searches and I was pleasantly suprised to find that the toolbar actually did the conversion without me having to hit the Search button.

Doesn't get much easier than that...try it for yourself.