If you like that type of thing, you'll love Mathematica. Although its price history traces an unbounded exponential curve, there is a free reader that can parse the many examples of Mathematica at work.
Not everything about it is wonderful. Sore points include syntax. In almost all respects though it's pure art, and highly productive, best in class by at least an order of magnitude. It most definitely supports a declarative programming style and that is the best way to use it.
I'm looking forward to open source competition. One of the keys will be good graphics, as for example supplied by the LGPL Smoke Vector Graphics library. However I doubt that the graphic, numeric, symbolic, typographic, and PL efforts required to hold a candle to Mathematica will ever come together properly. The languages are there but not the combination, not yet. Perhaps if some angel investor wants it bad enough, like Chandler.