So you want to track if your email is opened by the recipient – and you are using Outlook.. Then this is for you:
http://attachmetric.com/tutorials/

This might be more mailinglist oriented:
http://www.politemail.com/features/OutlookEmailTracking_Screen.aspx

Subscription service: http://www.mailinfo.com/web/

BUT wait for it…. There is a free option as well. 🙂 Check out http://www.spypig.com/