This page contains plugins for use with ParaView. The ParaView CVS repository contains many examples in the Plugins directory.
Generic Data Set
If you would like to add new cell types to VTK that violate the assumptions that the unstructured grid and polydata classes make, this plugin illustrates what's required. The Skeleton subdirectory contains empty implementations of the classes required for creating a new mesh type. The main directory contains an implementation of many of the members and a small test program that provide interpolation of attributes defined by values attached to edges and faces instead of the traditional VTK point and cell data.