Twitter for iPhone and iPad (free, universal) has been updated to version 4.2. This update introduces a number of changes, including an improved discover feature. Now, the app shows an activity feed displaying which of your tweets have been favorited or re-tweeted by other users. You'll find activity listed below the other discover features.
Search has been improved too, with auto spell correction in the search field and search history. New push notification options let you know when one of your tweets has been re-tweeted or favorited; an additional alert announces a new follower.
Finally, Twitter for iOS 4.2 offers support for Swedish, Norwegian, Danish, Finnish and Polish. You'll find it in the App Store now.