Gmail Notifr

Gmail Notifr sends you notifications about the received e-mails and other events in your Google account. It supports multiple accounts, checks mail at a specified interval, has Growl and sound notifications and has no background daemon processes installed as Google’s official notifier. Requirements: Mac OS X 10.5+ (Leopard).

Growl

Growl is a notification system for Mac OS X: it allows applications that support Growl to send you notifications. Growl offers you complete control over which notifications are shown and how they are displayed. You will not receive any notifications that you do not want, because you can easily turn notifications (specific ones or all of them) off. Growl requires Mac OS X 10.4 or higher.