If you own Ulysses III, check out the latest 1.2 upgrade. The export module based on CSS allows styled exports of RTF docs for Pages & Word as well as PDF, ePub & HTML. The way they've extended standard CSS for RTF docs is really intuitive to it's really easy to get into.
The only real downside I've encountered is that the latest version of Pages no longer opens RTF docs directly so you'll need a copy of Word or the iWork 09 suite to take advantage.
Here's the ref pages: Ulysses Style Sheets Reference
The really great thing is that Ulysses is coming to IOS very soon (and features the same export engine) so hopefully they'll implement a URL scheme so we can access it's loveliness directly from Editorial. They'll obviously need to find a way of exporting directly to the IOS7 version of Pages (rather than via IOS7) but I'm sure it's on the developers radar.
My favourite innovation in the world of Markdown since Editorial. :)