Been having lots of fun with this, here are the nodes I've made:
Gray noise:
randomly mixes each pixel on the output between the two inputs.
For use with directional blur. Makes each point point toward the center. Offset rotates these.
Regulate:
Makes the pixels be 'regular' as in regular polygons, snapping them to repeating values and also looping them after a certain value. This is basically just a neat way of rounding numbers thrown in with the modulo function.
Distance:
Gets the distance (abs(a-b)) between the two inputs.
Lump:
Highlights pixels of around a certain brightness. Named as such due to how it looks when graphed:
More hill shaped really, but lump sounded better.
Edge Distance:
Tries to get the distance from a dark spot each pixel is. Lags exponentially with tile size, not sure how to optimize it. :/
Lerp:
Linearly interpolates between two inputs, based on a third input. If t is 0, it returns the first one. If t is 1, it returns the second one. If t is anywhere in between, it returns a mix of the two inputs. Each input is an input parameter.
http://pastebin.com/s2tCfU8K
Square pattern:
Gives a chessboard type pattern, with the option for more than two colors. Due to a weird bug, the only sizes that don't have strange artifacting are numbers in 2^x, so the size input uses that.
(Note: there were some visual errors with the nodes that have been fixed since the pictures were taken.)
Been having fun with this tool, keep on accidentally calling it a game. Hope people find these useful!
edit: some more:
Inflate Heightmap:
This raises up a texture by a heightmap. Not pictured is also an option to set whether it loops off the top of the image or not.
Good for visualizing heightmaps you make. Note that without a surface input it will all be one color, shading just came from the lighting node.
Vector to Direction and Direction to Vector:
Don't know how often these would be useful, but I made these too.