As listeners of Directional may have guessed at this point, espresso is my favorite coffee drink. Living in Italy and being extremely conservative with my espresso choices, I've never got into coffee-related iPhone apps (I don't have a fancy coffee-making ritual; it's just an espresso machine), but Great Coffee App is, as the rather bland name implies, actually pretty great.
Great Coffee App provides an introduction to 16 popular espresso-based drinks. The app is delightfully skeuomorphic in its presentation of espressos and coffee cups; there's some nice background music when you browse the main screen, but it can be disabled. In the app, you'll find descriptions and interesting facts for the classic espresso, the espresso lungo, the macchiato, as well as the more peculiar Irish Coffee and Cafeccino; you can tap on each drink and see zoomed-in view of its ingredients and layers. For each drink, the app comes with good localized descriptions (at least based on what I saw for the English and Italian versions), and a downloadable video showing the preparation process.
I found Great Coffee App to be beautifully done, informative, and a great visual introduction to popular espresso-based drinks. It's only $2.99 on the App Store.