Trying an iOS app called “ByWord” that is mostly focused on being a text editor but also has a WP plugin.
Here’s an image: me doodling in the margins of Urth of the New Sun last night. There’s no inline preview.
The main thing about this is that it supports Markdown as its text markup interface. Which would be a lot more useful with a real keyboard, though it does offer a toolbar for all of that kind of stuff.
edit: Okay, if you used any images you have to tell it to upload them, it won’t do that automatically. It also doesn’t make any allowances for editing your post afterwards. It’s a really nice environment for writing in but those are both kind of dealbreakers for my intended use as a WP client. Oh well.