iOS: Mail Pilot was a handy email app that allowed you to turn your emails into tasks so you could remember to deal with them. It was useful, but it was also a little clunky to use. Mail Pilot 2 fixes most of those problems by adding a lot of gestures.
The main problem with Mail Pilot was the cluttered icons that made it difficult to get things done quickly. Mail Pilot 2 replaces those with gestures so you can easily assign emails into different sections, including done, save for later or set up a reminder. Overall, the new interface is pretty solid, but you might find yourself making errant swipes now and again.
Perhaps most importantly (at least in the iOS email app space), Mail Pilot supports all IMAP accounts, including Exchange. It's not compatible with any POP accounts, but considering how limited most iOS email apps are, it's a nice touch.
Mail Pilot 2 ($9.99) [iTunes App Store]