Shadertoy is a showcase of WebGL and shader talent. Using WebGL and fragment shaders, animations and some at-times astounding graphical effects can be created and shared online.
Well, I had to have a little play. One simple plasma shader. You can mouse-over the image above to access the play/pause button, or click the title to go to the project page. From there you can view the (not all that complex) code used to produce it.
WebGL requires a HTML5 browser (any modern browser is already compatible). If you have an OpenGL compatible graphics card (most graphics chipsets are), the rendering code will run on the GPU at a vastly accelerated rate.