The Lissajous Lab -- This one uses physics stuff
      (It might crash your browser, but it's worth the risk!)

Super Spiro -- This one uses geometry and polyhedra

Cursor -- This one uses geometry and lines

Splash! -- This one uses trigonometry

  3D Wire Frame -- This one uses geometry and polyhedra

Space Flight -- Use your mouse to fly around through space.

Amazing Spiro -- Make really cool pictures with geometry

Encylcogram -- Make spirograph-type pictures with geometry

Be sure to check out my stuff on fractals too...
These are the coolest math pictures of all!