Wikimedia Foundation has released the official Android app for Wikipedia in the Android Market recently. Although there have been several apps that lets go read Wiki content on-the-go but who needs third-party apps when you have official app.
As you would expect, it is completely free and gives you access to all the 20million articles available on Wikipedia and across the languages.
You can also save articles for offline reading, search for nearby articles on the map, or change the default language for accessing the articles.
As this is the first version, we would expect Wiki team to improve the app further to increase the usability as well as make use of all the functions available on Android devices. As one commentator in Android Market points out that adding a feature to open all the Wiki URLs directly in the app would be certainly a good addition in the next version.
Android Market Link