These are all some fun effects I've come up with in processing.

4drot:
This is a unit hypercube rotating on 4 different axes, which is the projected orthgonaly into 3d, and the perspective projection into 2d. All using math, no D3D or OPENGL mode for this. The screen blur is also fun. Try using the up and down arrows to change the noise of the edges. It's a neat effect.

tunnel:
A standard oldschool demoscene effect that I love to recreate. The entire tunnel is "raytraced" during setup and then some fun hacks are used to fake the motion. One of my fav effects.

diffcloud:
Always wondered how that difference cloud algorithm worked in Photoshop. Turns out it's aptly named. It's the absolute difference of two perlin clouds, or rather the current image and a perlin cloud. I animated this one for fun. Good fun. Kinda slow though, it's begging for SIMD.

plasma:
One of my favourite effects, applying a sin map to a palette and some low octave noise can work magic. And when you threshold it, BOOM! plasma worms. Fun times.