What are some good examples of procedural or screen-space pixel shader effects? No code is necessary; I'm just looking for inspiration.
In particular, I'm looking for effects that are not dependent on geometry or the rest of the scene (so they would look okay rendered alone on a quad) and are not based on image processing (they don't require a "base image," though they can incorporate textures). Multi-pass or single-pass is fine. Screenshots or videos would be ideal, but ideas work too.
Here are a few examples of what I'm looking for (all from the RenderMonkey samples):
I'm aware of this question; I'm not asking for a source of actual shader implementations but instead for some inspirational ideas -- and the ones at the NVIDIA Shader Library mostly require a scene or are image processing effects.