Android Push Notification By GCM (Google Cloud Messaging for Android (GCM) )

Google Cloud Messaging for Android (GCM) is a service that helps developers send data from servers to their Android applications on Android devices. This could be a lightweight message telling the Android application that there is new data to be fetched from the server (for instance, a movie uploaded by a friend), or it could be a message containing up to 4kb of payload data (so apps like instant messaging can consume the message directly). The GCM service handles all aspects of queueing of messages and delivery to the target Android application running on the target device
This document describes how to write an Android application and the server-side logic, using the helper libraries (client and server) provided by GCM.
Check these links,
http://developer.android.com/guide/google/gcm/gs.html
http://developer.android.com/guide/google/gcm/demo.html
http://www.basic4ppc.com/forum/basic4android-getting-started-tutorials/19226-android-push-notification-gcm-framework-tutorial.html
http://fundroiding.wordpress.com/2012/06/29/google-cloud-messaging-for-android-gcm-simple-tutorial/
for client side app you can find the code here
https://github.com/marknutter/GCM-Cordova