yewknee.com

Photoshop Filter Forge

Filter Forge is a plugin for Adobe Photoshop that allows users to build their own plugins via a "node-based editor." People can also submit their filters to the site for others to download. Honestly, out of the 400 submitted plugins I doubt you could find 15 that you would really want to use on even a semi-semi-regular basis but occasionally there is something worth looking at (most are not... gross).