This is a quick one. I don't remember where I heard about this software, so I can't properly credit the source. But I recently came across a really great bit of code called WriteRoom from Hog Bay Software. It's designed to do one thing and do it really well. You write. That's it. No fancy tables, formatting, indexing, footnotes, blah, blah, blah. You write. I'm using it right now, in fact. My favorite feature is the full screen mode, which blacks out your entire screen and displays your text in the font and color of your choice (default is Monaco green, I like Helvetica green). It's like an old terminal word processor. Even the "cursor" is a flashing translucent box. The publisher bills it as "distraction-free writing." It'd say they're spot on.
I have learned to really appreciate the distraction-free writing style. Because I'm slightly ADD, when I sit down to write, I find myself checking my e-mail, looking up web pages, tweaking my to-do list, etc.. Spaces helps a bit (one of my favorite features of Leopard), but the desktop beckons. In WriteRoom, I am alone with my words. I rather like it. It's a deal, too at $25. It even spell checks on the fly, and auto-saves every 5 minutes (user definable).
It won't auto-number pages, draw funny shapes, include clip art (thankfully), track changes, or color your text every color of the rainbow. But it will help you write. And that's all-write with me (sorry, I couldn't resist!).