qc is a command line tool that calculates in-line math expressions with no pipes or command line tricks. The result of the calculation is displayed in the the command line and automatically copied to the clipboard for easy of use.
A handy way to use Python’s maths library at the command line.
Soulver is a new kind of calculator application which uses a simple yet powerful word-processor style interface instead of the traditional “button” approach to doing math.
Update 21/04/10: As itohsnap pointed out on Twitter, there’s one thing wrong in that screenshot. In Soulver’s defence, it gets the right answer if you tell it to do k / q. The fact I didn’t notice is why I need a calculator in the first place.