MathViz is a straightforward OS X application that allows you to effortlessly visualize any function of two variables y=f(x,z) in brilliant colors.
There are a couple of pre-built functions, and you can add your custom function and visualize it.
You can rotate around all 3 axis (X, Y and Z) as well as zoom in and out using the controls.
Powered by TExpressionParser - a flexible and fast expression parser for logical and mathematical functions by Egbert van Nes, with contributions by John Bultena and Ralf Junker.
NOTE: To download MathViz via the App Store an Apple account is required.