I spent a bit of time suring the web trying to find as many plugins as I could for Windows Live Writer.  Part of my search included finding tutorials for writing my own plugin.

The following are some of the resources I found:

Writing Plugins for Windows Live Writer - Getting Started

Writing Plugins for Windows Live Writer - Adding an Icon

Coding4Fun hardware Boneyard - Using the CuteCat with .NET

Windows Live Writer Plugins Collection - Release Cyclone

Windows Live Writer Team blog

Windows Live Writer Development Forum