Just bundled up a new release of Geany Dark Scheme (http://code.google.com/p/geany-dark-scheme/) - this adds support for Markdown text files and NSIS scripts, contributed by pho3nixf1re84 and mr.soup12.
The scheme currently supports highlighting for these (26!) languages:
.c - C languages files (contributed by Paulo Cabido)
.cs - C# language files (contributed by Duncan Lock)