[yjftsjthsd-h]

I know it's extreme, but Notepad. Literally and unironically; write in markdown, and it should work.

[WalterGR]

No. If for absolutely no other reason, through Windows 7 at least, Notepad allows you to undo only the last thing you've done. That's a perfect, one ingredient recipe for inevitably losing work.

[themodelplumber]

Notepad++, PSPad, AkelPad, Notepad2, and SciTE are all free & good replacements for stock Notepad.