DateTimePicker (by Boguslav Brandys, Poland) - analogue of the corresponding component from VCL for date / time selection.
MHMonthCalendar (by D. Zharov aka Gandalf) - a calendar for placing on a form (this is exactly what is called from the DateTimePicker component by clicking on a special button, but in the form of a separate modal dialog).
KOLMonthCalendar (author E. Mikhailichenko aka ECM) - another implementation of the calendar.