The previous post explain how to "Create and Obtain API Key for Google Maps Android API v2 service". In my trial experience, you need a debug API Key, for your testing. Means you test on your device connected with PC and download from Eclipse.
To generate debug API key, repeat the steps in the post "Create and Obtain API Key for Google Maps Android API v2 service", with debug certificate fingerprint (described in the post "Displaying the SHA1 certificate fingerprint") instead of release certificate fingerprint. The output should be like this:
In my test, both API Key (Key for Android apps (with certificates) and Key for browser apps (with referers)) can display map.
A simple example using Google Maps Android API v2, step by step.