[deninho]

Just that. Maybe Word in the first place, for the spell checking. But, other than that, just use it as a plain text editor.

I also find it useful to create a new file for each chapter.

[kwhitefoot]

You don't need Word for spell checking. For instance, Emacs can use ISpell, ASpell, etc.

[deninho]

Good to know. I'll check if Sublime Text supports spell checking as well :)

[mpolsz]

And in emacs you can use org mode with export to pdf though latex