There are three computational tools that I would like to know well. The tools are SketchUp, ArcGIS, and Mathematica. They successfully map the user's mental model of the problem to the tool's control leavers for a solution. In the hands of a skilled practitioner incredible results are accomplished. The blog posting The Incredible Convenience of Mathematica Image Processing is a reminder of this. This is inspiring as a potential user and humbling as a software developer.
Found via Tufte blog.