[bhickey]

Not a side-scroller, but here's a screenshot from a terrain generator that I wrote:

http://i.imgur.com/HgMWbXe.png

the white dot in the center is a control point that the user can drag around. That point defines a mountain. Height decays exponentially with distance from the control point. The height function is perturbed by an underlying noise function.

Edit: It's all done in JS/WebGL using a fragment shader and blatting the output onto static canvas elements. These are then composited for the larger image. It supports scrolling and zooming. I could never get the performance quite to where I wanted it.