I'm going to stray from the beaten path and suggest that a full-featured text editor like Vim or Emacs may be appropriate for some people. I use Vim and like it a lot.
Vim makes it easy to move sentences and paragraphs around with simple keystroke commands. It is easy to deal with multiple files in Vim. You can organize your project into as many files as you want, and insert files in your document wherever you want with a simple keystroke command, without having to open the inserted file first. You can "fold" your documents into chapters if you want, which makes each chapter (or scene, paragraph, whatever) appear as a single line on the screen. You open and close the folds with a keystroke command to work on them. Folding is great for high-level organization. You can also mark, using all the letters of the alphabet and more, different places in your document, there are movement commands to get you to the beginning of the document, end, mark a, mark b, next paragraph, etc. There are too many more useful features here to list. No matter what you do to the document, it is still a plain text file in Vim, ready to format later. The learning curve for Vim is steep, and the documentation is scary, because Vim was made for computer programmers, but writers only need to learn a very small subset of what Vim can do to be productive.
I've gotten away from the Words and OpenOffices of the world as much as I can, although I do use OpenOffice quite a lot for some jobs. My rule is that formatting a document is the absolute last thing that I want to do, because undoing improper or unwanted formatting is such a pain in the behind. Modern word processors are designed to trap writers into unwanted formatting. So I write with a text editor, and format later. Vim is faster and easier than a word processor anyway.
Vim will be the first choice of only a very few people, but for those who can get past the initial frustration and learn enough to be productive with Vim, it is awesome. Best.