If you like patch based tools and experimental visuals you might want to check out FilterForge a new Photoshop plugin which also works as a standalone application. Currently it's in beta and you can register at their site to apply for a free evaluation copy.

FilterForge allows you to create all kinds of textures or effects by simply connecting various functional modules with "cables" - a system that is very common in a lot of 3d software or visual programming tools like max/msp or Quartz Composer.

Some features that I find very interesting are: the resulting patterns can be made seamless, they can be up to 32000x32000 pixels in size and there is an optional intelligent antialiasing algorithm that smoothes out jaggies at high contrast edges.

You can share the filters and effects that you build on the FilterForge website and if you deliver good ones that many others find useful you can even get FilterForge for free.