Highly recommended: Scribble Papers.

It's an extended editor, more like a cardbox. I quit using editors like notepad for text transfers to InDesign altogether because this little program is so extremely useful. Best thing is that you can collect all texts for a project at single pages each in one folder without having to save each single file separately. Of course you can export the pages or folders as well, if you prefer. Can't imagine ever living without ...

At the moment it's in german, but there are icons, too, and actually you don't need the menu, because if you're accustomed to work with windows explorer, you'll understand scribble papers as well.

http://www.scribblepapers.de.vu/

I love textpad. It supports regex, has tabbed, savable workspaces, and doesn't hog my ram.

The best text editor I've ever used is my beloved UltraEdit (for Windows). Adam Twardoch also swears by it.

I use Notepad for testing complex script OpenType fonts, because there is less application architecture between the font and the output, so it is a more reliable environment to confirm exactly what the Uniscribe text engine is doing for a given writing system.

Tex-Edit Plus is my right hand.

TextWrangler always, SubEthaEdit sometimes and Pages (gasp!) for pointedly not using Word, not choosing to annoy myself and to have a bit of fun while I'm at it.

Pico when pressed. Please don't say vi or emacs.

Web input forms. Especially in OmniWeb 5.

All that said though... with most of the text that I handle, it seems people don't edit their text, text editor or not.