Gmail Dock

Gmail Dock is not your ordinary Gmail client. It is designed with the realization that the best way to do most tasks in Gmail is to use the web.
The web-based Gmail client gets new features before most desktop clients, and it provides a great user experience.

Still, it would be nice if Gmail integrated more deeply with Mac OS X. That’s what Gmail Dock is about.
Features
Easy, one-click access to your Gmail account
New mail notifications with Growl and sound options
Handling of mailto: links from any browser or application, systemwide
Global, customizable hotkeys
Support for Google Apps for your domain
A touch of polish