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.
“Incredibly powerful texture engine.”
“It's a powerful and logical way of creating effects that's relatively easy to learn by seeing how other effects are built. Creating filters from scratch is time-consuming, but for a wider user group, it's a great way to modify already-created effects.”