This is my favorite Freeware Calendar app.
Mozilla Sunbird
Mozilla Sunbird? is a cross-platform calendar application, built upon Mozilla Toolkit. Our goal is to bring Mozilla-style ease-of-use to your calendar.
http://www.mozilla.org/projects/calendar/sunbird/index.html
Holiday plugin to Sunbird that inputs all the holidays (ie Christian, jewish, etc..)
http://www.mozilla.org/projects/calendar/holidays.html