There are probably other ones posted here, but I've used this one before. The attached database contains a custom calendar that was made by Allen Browne (I think). This one populates a form textbox after a date is selected. There is also one for displaying a message box to look at. It's called "SAcalendar"...

The second database is a calendar that I created a long time ago. It's really bland looking but works great and is not really that complex with respect to coding.