I hacked this together mostly for personal use, so it is far from perfect! But feel free to fork and extend :-)

This editor features:

• All features a good editor should have: Keyboard shortcuts, copy, paste, undo, redo, save file, open file, ...
• GUI with side-to-side edit and preview panel
• Spell checking
• A Tree view which shows the document structure
• Support for MultiMarkdown to get Maths, Tables etc. working
• Export of HTML

the obligatory screenshot:

Set the absolute path of the Markdown executable in the default.cfg file.

• Ctrl-C, Ctrl-X and Ctrl-V - the obvious text operations
• Ctrl-N, Ctrl-O and Ctrl-S - New, Open and Save...
• Ctrl+F - Find in text
• Ctrl+T - Toggle Preview
• Ctrl+E - Export HTML file
• Ctrl+Q - Exit

• PySide (GUI)
• PyEnchant (Spell checking)
• MultiMarkdown or any other Markdown parser