Update: 2016 Calendar Now Out!
I created a Catholic Holy Days of Obligation calendar for the year 2015, which you can download at:
Catholic Holy Days of Obligation calendar for 2015 (.ICS file, suitable for importing into iCal or Outlook).
It's based on About.com's list of Holy Days of Obligation by Scott P. Richert. Again this year, it also includes embedded links, so you can read more about each Holy Day. And it includes reminders the day prior to each event. This year, I used Maru's iCal event maker to create the calendar in about 10 minutes. Really quick and easy! If you find any errors, please let me know.