Plugin Commander  
Free version available
Program for organizing, using and creating filters. 

Redfield Plugins  
You can make some beautiful backgrounds with these.
Jama 2000
Jama 3D   Mesh 3D
These two are free plugins
Lattice Composer
Free plugin for grids and netting effects

   
Demo available with 2 free plugins
Set of 20 plugins which includes over 120 basic effects.
Free Graphic Tools  

The Plugin Site Forums  

Reptile 2   
Free program for creating surfaces and textures