What's a good calendar/alerter app?

This will be for windows. Multi-year preferred since I don't forget when the date comes a couple years from now. Freeware or cheap preferred. The best comparison I can make is Groupwise, but I already have an existing email client - Thunderbird. That just made me do a search now and I'm seeing what is a good looking mozilla project, Sunlight and Lightning. Any experience with these?