In this vein, there's a time-management technique, called the Pomodoro Technique, that consists of dividing your work into chunks of 25 minutes called pomodoros, alternating short breaks in between them.
CherryTomato is an application that helps you use this technique and manage your pomodoros, crossing them out when you're done.
The application works in the background, staying minimized on the system tray. You can access a tiny control panel to manage your pomodoros by just clicking on its icon.
From that same icon on the system tray you can start new pomodoros and access the application's settings. From there you can integrate it with Windows Live Messenger or Skype, and set up reminders.
Despite its simplicity, CherryTomato can be a really useful application for improving your work productivity.