Cloud to device messaging, Androids counterpart to push notifications, is pretty easy to implemented. In his C2DM tutorial Lars Vogel walks you through everything you need to know.
Creating Android Virtual Devices (AVDs)
In the second tutorial of 31 Days of Android you'll learn how to create Android Virtual Devices for the emulator.
Parcel data to pass between Activities using Parcelable classes
If you want to pass complex objects beween Activities you have to do a little ceremonial work (aka implement the parcable interface). In this tutorial you'll learn how to do that.
Ever wondered which parameters to stuff in an intent to share an email? Android Snippets got the answer!
Badges are a pretty common design pattern. Viewbadger is a simple way to "badge" any given Android view at runtime without having to cater for it in layout.
Smart Image View for Android
SmartImageView is a drop-in replacement for Android’s standard ImageView which additionally allows images to be loaded from URLs or the user’s contact address book. Images are cached to memory and to disk for super fast loading.
Google just announced significant updates to their (painfully slow) emulator. That should make testing more pleasant. If you need even more speed then try one of those Android x86 images that can be found on http://www.android-x86.org/
Good read on how the Android App Papermill worked. Papermill is a client for Instapaper.
We covered this already, but now currents is available for the outside US markets.