We've talked about Articles here on the site before. Out of all of the apps that won Apple Design Awards this year, I would say it's probably the most underrated and most useful. It's a Wikipedia reader, which doesn't sound like much since the mobile version of Wikipedia is pretty good already. Having a dedicated app for the open source encyclopedia makes a surprising difference, though, and it allows you to consume all of that content in a really focused way. There are integrated maps and photos and lots of different ways to browse information, including shaking the iPhone to see a random page.
The new update doesn't hurt either; version 1.3 adds a language picker, a new Table of Contents sheet, and an orientation lock that even works on the iPhone (a previous update already made the app all ready for iOS 4.0 and the Retina Display). Articles is US$2.99, which might seem pricey to browse content that you can already read for free. However, if you've participated in a few marathon Wikipedia sessions just by following a few random reference links, it's well worth the purchase.