With the tide of plain text editors showing up in the app store, I'm getting a little soggy, and I know you might be, too. However, I have another one for your consideration: Note & Share (for both iPhone and iPad) adds some unique features to the standard mix, primarily from the "Share" half of the name.
First, like the recently-covered iPad app Edito, Note & Share supports Markdown and can render it for some of its output options, which include syncing the rendered HTML output to Evernote or sending it by email. The Evernote sync is of interest to me as an Evernote fan, but so is the Dropbox sync that it provides. Dropbox -- which is quickly taking the lead as the preferred method for both syncing and sharing -- works superbly for text files because, among other reasons, they end up fully-indexed in Spotlight on your Mac.
Note & Share can also send to Twitter or Plurk and save to its own database. Of interest to Japanese users is its support for ATOK, a fast Japanese input method, to which it can send files and then retrieve them after editing. It also has a bookmarklet for Mobile Safari that will send a shortened URL to your document for linking.
The app lacks the super-handy, extra Markdown toolbar of Edito, but its developers tell me that they're exploring the possibilities there. Beyond that, the Markdown support is great. The sharing options only show buttons if you have them enabled, so your interface only contains what you need, not a bunch of grayed-out options. At US$1.99, it looks like a great option for handling your iPad (and iPhone) text editing, especially if your notes need to go to more than one place. Give it a shot if you haven't already nailed down your editor of choice.