Yin-Yang

Shamelessly stolen from Apple's graphing calculator demo.

r = Sqrt[x^2 + y^2]; 
theta = If[x > 0, ArcTan[y/x], 
    If[y > 0, ArcTan[y/x] + Pi, ArcTan[y/x] - Pi]]; 
YinYang = If[r < 1.6, (Cos[theta - r] - Sin[theta])
    (r^4 - 2 r^2 Cos[2 theta + 2.4] + 0.9) + (0.62 r)^1000, 1]; 
ContourPlot[YinYang, {x, -2, 2}, {y, -2, 2}, 
    PlotPoints -> 200, Contours -> {0}, Frame -> False];