I'm in the same boat, and use this: https://github.com/panicsteve/nv/downloads

This fork of Notational Velocity adds a third pane which shows formatting using markdown.

If you are willing to learn markdown, and it's pretty darn easy, you can add formatting while maintaining raw text format.

I like markdown enough though that I find I write in markdown, and just hide the preview pane that includes formatting. I just don't really need it.