GIST is the fastest way to check multiple Gmail inboxes for unread messages.

Replace "emails = ['example@gmail.com', 'example2@gmail.com']" in gist.py with your Gmail addresses. Works for Google Apps accounts too.

Run 'python gist.py'

Type 'login' to authenticate your accounts,
'go' to list unread messages,
'open #' to open the account that has the # index in your web browser,
and 'quit' to exit GIST.

Keep your Terminal window open all day for best effect.