Filter Forge is – by quite a margin – the most powerful plug-in we've looked at here. That's because it's a tool for creating plug-ins, both generative texture-creation tools and effect filters.
“Chief among my pleasures is Filter Forge, which I've been ranting (positively) and raving (voraciously) about ever since it entered my life.”
Resident Enlightenment Manager Linden Lab, makers of virtual world Second Life
“For 3D modelers, Filter Forge is a dream come true. It creates seamless textures with a single mouse click. The professional version creates the following map types for any texture: bump, normal, specular strength, specular exponent, diffuse, metallic, and alpha. The same filter can be used to generate any resolution, since filters are procedural.”