Another great, simple product from the folks at 37 Signals: Writeboard is live :
Writeboard is a web-based writing tool. It lets you simply write, share, revise, and compare text. With Writeboard you can write solo or collaborate with as many people as you’d like. Writeboard isn’t about heavy text formatting, or WYSIWYG, it’s about the text itself. The words on the page. If you care about design and layout, you’re best bet is to take the finalized text from a writeboard and import it into a page layout program. Make your magic in the right tool.