[edp]

You made me check but there is a "birthday" field on the contact form and I can display a "Birthdays" calendar with events for the birthdays of my contacts.

[kqr]

For other types of anniversaries (like close friends' and relatives' wedding anniversaries) I sometimes create dummy contacts.

[meowster]

I just create an all-day calendar event and manually change the date each year.

[setopt]

Can you not just make it a yearly repeating event?