This is a slick little free app you can download for the iPad/iPhone to publish to PubWriter with.
Grab a copy at: https://itunes.apple.com/us/app/marklite-a-delicate-markdown-editor/id1098107145
It does't sync up with dropbox, although you can publish to dropbox. And I don't believe it supports snippets, which I am finding is a huge benefit of atom.io.