PEN

PEN(Pennocks Email Notifier) is a tool that notifies you of incoming mail.

The application runs in the system tray and periodically checks the status of your email inbox. If a new email arrives, you will be notified by a small popup window near the system tray, and you can optionally set up a sound notification.

You can set up multiple email accounts and set a different sound for each. The app will show you what's in the subject line, or the full content of the message. You even have the option to delete the selected email without having to download it.
The program supports POP3 ( and SSL) MAP, Gmail, AOL, Excite and Netscape protocols as well as other web mail services (Hotmail, MSN, Lycos, Yahoo and Mail.com).