I have two active Android apps on the Google Play Store. Both are relatively simple, featuring only a couple of views, but properly supporting different screen sizes. They are written in Java with the native Android SDK.
PlusFive is a native reader for the popular tech news site Slashdot. Unlike the mobile version of the site, the app looks very similar to the classic desktop version of Slashdot. It supports reading the news stories and commenting on them, as well as reading and filtering the comments. The name is a reference to the highest score a comment can achieve.
Personal Volume allows you to adjust the in-call talking volume separately for some contacts. It is useful when talking with certain people who speak very loudly or very quietly. The configuration is simple, and the app can run in automatic mode in which it saves the volume per contact whenever you change it during a call.