Everyone else has had just three choice Mac apps, but I'm going to claim four because two of my choices live in the Menu Bar, and are therefore very small. Only you and I need to keep count, though, eh?
This marvelous little rich text editor is an excellent tool for writing to word counts, something I have to do very often. Bean packs in a lot of great features, and the developer is responsive to feedback and suggestions.
When I'm not writing to word counts, I'm usually using Markdown to write for the web. Until last week I'd been using TextMate for this, exclusively, for a couple of years. Now, with the release of BBEdit 9.0, I'm wavering between the two. Both are wonderful, and writing with Markdown just isn't the same without one of them to help me out.
I'm one of those weirdos who likes to keep the Dock out of sight most of the time. I don't use it for launching or switching apps, and I don't use it to keep minimised windows in either. But there are some functions that I like to have in easy reach from anywhere, and that's why I'm a big fan of Menu Bar applications. That said, there's not a lot of Menu Bar to be had on a little MacBook screen, so I'm very picky about which ones get the honor of a place up there. I Love Stars earns a spot. It does nothing but let me assign ratings to songs, but in my opinion it does it very well and, most importantly, sits in the best place for doing it.
Another one from the Menu Bar, and this time it's a clipboard history utility that saves my backside 27 times every week. At least. It only saves text, but that's fine for me because that's what matters most in my line of work. With Jumpcut running (and it's always running), I can merrily copy umpteen things from a dozen different places and be sure of pasting them easily, and in the correct places, in the text document I'm writing at the time (see Bean and BBMate raves above).
OK, that was five. Sorry.