For you Mozilla/Firefox users:

Beer oclock » Overview

A small beer icon appears in the status bar of your browser which periodically alerts you to the time until your office beer o'clock: "17 hours 'til beer o'clock".

Messages are not just displayed in hours and minutes, but other time-frames that may be more relevant to you and your office fellows: "15 cups of coffee 'til beer o'clock", "3500 lines of code 'til beer o'clock", "10 ridiculous questions from clients 'til beer o'clock". You can also add your own messages for non-stop beer/office fun.

https://addons.mozilla.org/firefox/732/