Password Monitor is a somewhat new look on a tool that has been in production in a number of environments for awhile. According to the site:
Password Monitor is a simple utility that will count down the days until a user’s Active Directory password is due to expire. An OS X 10.5 (or newer) system properly bound to an Active Directory is the only requirement. Additional features include the ability to display the exact expiration date on the logon window (admin rights required) and to automatically launch the utility at startup. The number of days between required password changes has to be manually set in the preferences. The range has to be between 5 and 365 days. The default is 60 days.