The WordPress iPhone application, available from the app store, is quite nice. It can connect to both wordpress.com and self hosted blogs, and can handle multiple blogs.
The edit interface shows html code, no fancy editors.
Drafts are initially stored locally, for reliable offline editing; and the usual publishing status categories are applied when uploading.
I’m writing this on the train home from Uni, not sure how good it would be for start to finish writing of long posts, but for quick notes, photo posts and minor alterations of existing drafts, this app beats the web interface in my opinion (which also only works with the HTML view!).
(PS: I used the web interface to add the photo gallery!)
