I've been a Mac person for two or three years now, but I haven't purchased much in the way of software. I do have Scrivener and enjoy writing with it. I originally purchased iWork for Pages and that's one I could have done without (especially after I found Scrivener). I also have Open Office (free).
As much as I hate to say it, I may eventually buy MS Word. It's been a pain going back and forth with editors and beta readers who are Windows based. (Though I can open Word files, I can't see tracking changes and notes and such.)
I'm sure more software-savvy folks will have ideas for you. I tend to just use what I've got unless something's ticking me off, heh.
~Lindsay
P.S. I recently added Kindle for the Mac, for when I feel like reading ebooks on a big screen.