Linden

android-formidable-validation. Form validation and feedback library for Android. Provides .setText for more than just TextView and EditText widgets. Provides easy means to validate with dependencies.

android-tandemactivities. MapFragment library for Android (also can help you use any other Activity in tandem with a FragmentActivity). Includes small example app that shows some solutions for back button and fragment backstack issues that stem from MapFragment solution.

Crouton. Context sensitive notifications for Android

android-async-http. An Asynchronous HTTP Library for Android

datetimepicker. DateTimePicker is a library which contains the beautiful DatePicker that can be seen in the new Google Agenda app. (Currently working on the TimePicker)