MarkdownMail is an excellent application by Secondgear Software (which we previewed here) that allows you to write in Markdown and export via email in perfectly formatted HTML code. The iPhone version featured a great icon, a polished UI, a basic yet powerful feature set.
Secondgear Software just released the 2.0 version of the app, which introduces native iPad support (the UI is similar to Mail, with sidebar / popover), support for editing and saving drafts and the possibility to email a raw Markdown formatted post. This is very useful if you consider that blogging platforms like Posterous or Tumblr accept post via email in Markdown format. In this way, MarkdownMail has become some sort of a blogging app, too.
Other features include the possibility to copy the generated HTML code to the clipboard and voice-over friendly navigation.
MarkdownMail is one my favorite apps, both on the iPhone and iPad. $3.99 in the App Store, universal.