Shader to flip image on both x and x axies. Can just do one as well... unconventional operation, but shows how shaders can be used to go through computationally complex images and perform operations quickly that are easily paralellized.
Another shader I figured out by just playing around on my own and attempting to recreate powerpoint transitions...could be animated later to mimic the actual effect. But the spirit is still there.
Another 'early' one that I made that just makes an image brighter by multipliying all of it's pixels by a constant. Apparently most image editing programs do this by interpolating a gray color with the target image.
Shader designed to convert color image to B&W. Inspiration drawn from Graphics Shaders: Theroy and Practice by Bailey and Cunningham.
Shader to add color tint to image. Made by just messing around with shaders.
Things I'd still like to do: