Add means to easily create a custom ‘New Post’ page

I have been searching through the plugins for ages trying to find an effective inline editor that I could customise to suit my needs but none of them appear to do this.

That is, enable the creation of new posts on a page which looks exactly like your active theme.

I am in the process of doing this using the wp_insert_post() function together with a custom implementation of TinyMCE, but it feels very messy.

I think this would be a very popular feature as it would mean you could update your blog without having to depart from its look and feel.