MacJournal is my favourite word processor on Mac OS X, which you might think odd because it is not designed to be one.
But as a professional writer I really enjoy the simplicity of the interface, and the way I can put all my writings into different categories (each journal acts as a text category).
It has spellchecking, word count, all the essential basics. It makes no demands on the user. You don't have to think of filenames and locations to save stuff in - you just click the save button and it's done. (For the paranoid, there is an option in the preferences to have everything automatically backed up as text files as well.)
I can use it for personal writing (which is always plain text or hand-coded HTML) or for work, because it lets me export single entries or entire journals into RTF or HTML if I want to. And it's rock-solid; I cannot think of a single time when MacJournal has crashed on me.
Word has more features but crashes like a penguin riding a bicycle (ie, all the time). AppleWorks is butt-ugly and slow. BBEdit Lite is lovely, swift and whizzy, but doesn't have a spell check and requires me to think about where I save each document and what I will call it.
MacJournal beats 'em all with its delightful simplicity and reliability.
Snarf it here:
http://homepage.mac.com/dschimpf/main.html