The DateTimeEditor which appears by default for a DateTime UltraGrid cell does not expose the underlying MonthCalendar control that is displayed when the dropdown appears (buse of a MonthCalendar limitation which was perceived as a bug in the DateTimeEditor, it became necessary to create a new instance of the control each time the dropdown appears).

I believe the UltraGrid exposes an event which fires after the dropdown appears; you might be able to use that event to get a reference to that MonthCalendar control via the UltraGrid's Controls collection, and then set its 'ShowToday' property to false. Note that I have never tried this, so I don't know if this will cause any painting issues.

An alternative would be to assign an UltraCalendarCombo instance to the column's EditorControl property, and remove the 'Today' button from its DateButtons collection.