I enjoy Dave Winer's outlining tools. I'm not fond of the often-used Twitter authentication (just personal preference; no technical reason), but the overall concept and work flow of the tools themselves is really nice.
I receive his daily blog post via email, so I have read a lot of his comments about "outliners" and how wonderful they are. It always leaves me scratching my head; I mean, doesn't MS Word (and MS Excel, for that matter) have outlining capabilities built-in? How many different ways are there to construct an outline?