Add as many blogs as you like and manage comments, posts and pages all from the app. Adding new pages and posts is as easy as editing existing ones. Best of all, you can delete, edit approve/unapprove and spam comments with a few taps.
Of course, not every blogger uses WordPress, and the other apps on the list acknowledge this. Shape Writer aims to make it easier to enter text by letting you trace the "shape" of a word rather than type its letters. Proper names and acronyms can be "taught" to the app by typing them once. They'll be traceable from that point on. Shape Writer costs $3.99US.
Also on the list is Jott, a voice-to-text app that records your voice, converts it to text and lets you send the result nearly anywhere, including a WordPress or Blogger blog (as well as Twitter, Facebook and more). I haven't tested it, so I can't speak for how well it works. If it does what it claims (speak up if you've used it), Jott for iPhone will make it much easier to publish long posts from your iPhone (provided that it supports your preferred platform). Jott for iPhone is free and requires a Jott Assist Plan, which starts at $3.95/mo. Mel reviewed the similar Voice on the Go service last week.
Visit wpbeginner for the rest of the list. As for me, I get a lot of use out of Instapaper (for reading reference articles when I'm away from my computer) and Evernote (pretty much the same reason) among others. If you want the simplest blog-from-your-iPhone solution, check out Posterous. All you need to do to set up and maintain a Posterous blog is send an email to firstname.lastname@example.org. It doesn't get simpler than that.