Easy way to get user to select and email address (or take default) from Google Accounts available on an Android device. See blog post here: http://www.entrepreneurskitchen.com/2013/02/getting-user-account-on-android.html

MyActivity.java

import com.google.android.gms.common.AccountPicker;
import android.accounts.AccountManager;

public class MyActivity extends Activity {
  
  // a number to distinguish this startActivityForResult from any others
  private static final int GET_GOOGLE_ACCOUNT = 1;
  
  @Override
  protected void onCreate(Bundle savedInstanceState) {
  	super.onCreate(savedInstanceState);
  
    // Inflate view, etc goes here
  
    // Call the AccountPicker Intent.
    // Change the "false" to "true" if you want the user to always be shown the
    // Activity, even if there's only one option (this allows them to add an 
    // Account at the same time, too)
    Intent accountIntent = AccountPicker.newChooseAccountIntent(null, null,
  		new String[] { "com.google" }, false, null, null, null, null);
  	startActivityForResult(accountIntent, GET_GOOGLE_ACCOUNT);
  }
  
  @Override
  public void onActivityResult(int requestCode, int resultCode, Intent data) {
  	super.onActivityResult(requestCode, resultCode, data);
  	if (requestCode == GET_GOOGLE_ACCOUNT && resultCode == RESULT_OK) {
  		doSomethingWithEmail(data.getStringExtra(AccountManager.KEY_ACCOUNT_NAME));
  	}
  }
  
  // rest of Activity
}