WriteMonkey for my creative writing needs, and VIM in a full-screen PuTTY session for my Web development work. That being the case, I'm all over the monospace, dark-background, focused editing scene.
OmmWriter attempts to take that aesthetic and make it somehow more spiritual, with three picturesque backgrounds and ambient background audio tracks (there are seven of each in the paid version).
I'm of two minds about this app. On the one hand, yes, it's beautiful. But if you want music as a background to your writing, why not pick your own soundtrack with Winamp or Foobar2000 running in the background?
OmmWriter also offers three keyboard-clicking sounds, which are kind of nice. None of these features are groundbreaking, really. OmmWriter could be seen as a way to gently ease into the world of distraction-free writing -- in case something like WriteMonkey's dark background is just too oppressive for you.
After the fold you can see a video showcasing several of OmmWriter's features and creative soundscapes.