iPad: You have a lot of choices for text editors on the iPad, but a large chunk of them keep things simple. That's fine, but if you're looking for a text editor with serious power, Editorial is what you're looking for.
At its core, Editorial is a Markdown-based text editor that syncs with Dropbox. But that's just the start. Editorial is incredibly customizable, so you can use it to write and edit just about anything you want. The kicker is its automation functions. Inside of Editorial is a Python interpreter and more than a dozen libraries of that automate images, scripts, HTTP requests, and plenty more. Essentially, you can create your own OS X Automator-style workflows inside of Editorial, and it's pretty easy to do with Editorial's Workflows. Editorial is a seriously powerful tool, and if you want to see the full depth of it, be sure to check out the massive MacStories review linked below.