Mail.appetizer is a plug-in for Apple's Mail and integrates seamlessly. The moment a new message is received, Mail.appetizer displays an onscreen notification window. It gives you a brief summary of the message, so you can determine whether the message requires your immediate attention. Thanks to your suggestions and ideas, the new version has many new features, including a resizable notification window to fit your desktop, custom font for the message body, displays sender's photo signature (from Address Book or .Mac), counter showing number of outstanding messages, and it shows mailbox name (optionally).
Mail.appetizer is no longer limited to your inbox. You'll receive notification for every incoming message, not including spam. The notification is shown after rules have been applied.