Parametron is a quick general-purpose calculator that graphs linear and parametric equations. It's great for fooling around with math and exploring the world of parametric equations. Make silly shapes, spirals, hearts, or scribbles. Also, it's excellent for prototyping graphs and double-checking analyses on the fly. It has built-in basic functions (exp, sin, cos, tan, asin, acos, atan, sqt, log, logt, abs, sinh, cosh, and tanh), the basic operators (+, - , *, /, ^), the ability to draw an indefinite number of graphs, animated graph drawing, and table generation all stuffed into a minimalistic, simple Android interface.
In short, it does almost everything your bulky TI-82 does, and it fits on a device that's never far from you.