The original Notify was , but developer Vibealicious has turned into a very capable, if still dead simple, e-mail client that sits in the menu bar. The user interface sports the same silver chrome as Safari 4 and Leopard, and it features tabs for each e-mail account to make it easier to tell which account you're reading or sending mail from. You can even send e-mail and preview entire messages from Notify's drop down user interface, without ever having to open a browser window.
There's support built-in for multitouch gestures to easily change tabs. For people who want to tweak exactly how they want to be informed as e-mail arrives, sound and visual notifications are fully customizable, and there's even an option to enable notifications.
Out of the box, the $10 Notify 2 Pro supports Gmail, Google Apps, Rackspace e-mail, MobileMe, and IMAP e-mail accounts, and it requires Mac OS X 10.5 or later. You have 14 days to try out all of its features on a trial basis, but you can run the app as a simple notifier alongside your current mail client for as long as you'd like.