Gmail Watcher is a gmail and google apps notifier that integrated into Ubuntu’s default messaging menu in top-panel. It supports multiple accounts and instant notifications.
provides packages for Ubuntu 10.04 Lucid, 10.10 Maverick, 11.04 Natty, 11.10 Oneiric, and 12.04 Precise. Just run commands in terminal to install from this ppa:
sudo apt-add-repository ppa:loneowais/gmailwatcher.dev sudo apt-get update sudo apt-get install gmailwatcher
After installation, you can find it in the messaging menu and then setup your gmail account. See the pics: