Here's a patch for a markdown lexer I wrote for use in the Geany editor. Patch against the latest from CVS with -p5. The original email to the Geany list is below:
I've created a basic Scintilla lexer for the Markdown formatting syntax along with Geany syntax and tag support. It doesn't do everything; indented code blocks and embedded HTML aren't highlighted, but it's already very useful. Some extra highlighting features are added for the Pandoc implementation: strikeout, using '#.' as a default ordered list item marker, and delimited code blocks.
Patch against build 4026 with -p5 from Geany's top build directory.
This was built and tested on Linux.