The once barren landscape of (good) Linux calculators has really changed recently. There is a new kid on the block and his name is SpeedCrunch. He's got some pretty nifty features. Its extremely user friendly, and designed by someone who actually uses a calculator, so you won't waste time trying to figure out which keys are what. Designed to be run entirely from the keyboard which is a huge plus. While it may not be as powerful as Qalculate it's an more than adequate for my needs. It's now in Fedora Extras so it's just a yum install away.