After years - or at least a few semesters - of lusting for it, I finally gave in and bought Mathematica. I purchased the Student Edition, which is just like the regular addition but cheaper, for $130; the regular edition is about $900.
Mathematica does so much cool stuff, I can't begin to understand or describe it all. It graphs stuff in 2 or 3 (and probably more) dimensions. It solves everything I've ever heard of and way more stuff I've never even heard of, not just numerically but algebraically. You can write animations, you can use it as a programming language, you can make fondue with it! (OK, maybe not that last one.)
Sally was curious whether Mathematica would prove useful or merely cool, and this is something I have thought about. In my dream life plan where I always take a math course, I can't see how Mathematica wouldn't be useful - it certainly would have helped me in most of the math courses I've ever taken, including the Geometry course I'm taking now. And in the even dreamier life where I become a math teacher, well, all the math teachers I've had recently have used Mathematica to make cool handouts, display animations to the class, and for assorted other nifty purposes. And I just really want this as a tool in my general arsenal of life.