MailCue is the must have mail notifier for your Mac. MailCue will help you process incoming mail quickly, and move on to other tasks. MailCue works with any IMAP provider, sitting in your menubar notifying you of incoming mail.
MailCue integrates right into your Gmail or mail provider with such features as, reply, reply to all, forward, full html or text message previews, support for embedded images, sending mail, account signatures, attachments, moving a message, mark a message as spam, putting an account to sleep, and more.
MailCue comes preconfigured for Gmail, Mobile Me, AOL, Rackspace, but supports any IMAP mail server.
MailCue has a detailed log panel, that allows you to see your account activity even if you step away from the computer.