Until recently I used Google Notifier to monitor my primary Google Apps inbox for new messages, and I used Apple’s Mail application to check my other accounts. Then I found Notify 2, a neat little Mac application that works even better.
Notify sits in your menu bar, up by the clock, and monitors multiple email accounts. It will check GMail, Google Apps, MobileMe, Rackspace, and generic IMAP boxes. When new messages come in, the number on the badge updates, and it can optionally make sounds or show Growl notifications.
If the ability to monitor multiple accounts isn’t enough for you, this feature will win you over: You can do basic email tasks right from Notify. You can press the spacebar to open a full preview of an email. You can delete messages, mark them as read, or even send quick messages. It’s cut down on the number of times I’ve had to actually visit my inbox, as I can trash and quick-view messages without loading up the web interface.
It’s $10 for the full version, with a trial, but the basic inbox monitoring features are still available after the trial period is over.