For a limited time (today?), iA Writer for iPad is on sale for $0.99 (regularly $4.99).

Writer has no graphical settings or formatting features. It avoids all distracting glitz in the user interface and puts all the beauty in the shape of the text. It uses an interactive logic that helps you concentrate, find your orientation and express yourself. For the iPad version we also added Dropbox synchronization, punctuation and arrow keys.

Apparently all the cool kids are using it. One of the unique features is 'Focus Mode':

Focus Mode blurs out everything except the current three lines of text you are working on. The idea is to activate it when you get stuck, blinding out everything else.

I don't have an iPad and am tempted to buy it on sale for if/when I do get an iPad.