Steve Dunn's Code Formatter Plugin for Widows Live Writer

Plugin formats and highlights source code, scripts, or anything else that has identifiers that can be coloured.

It uses different formatting 'engines'; in this release you get the choice of using ActiPro's CodeHighlighter or Alex Gorbatchev SyntaxHighlighter 2.0
Can place the output into Windows Live Writer as either HTML or Images.
Effects can be applied to images, such as shadows, glows, reflections etc.
Uses 'smart content' - which basically means that you can re-edit your code snippets, even after you've published them (e.g. highlight code and output it as HTML, then publish it, then re-load it and change it to an image and apply some image effects). A lot of plugins aren't 'smart content'; their output is raw HTML that can't be easily edited.