See DateTextBox for a discussion of supported date formats.
By default, a DateComboBox's dropdown icon is a downward-pointing arrow. This can be changed to a calendar icon to both suggest to the user which type of data the field accepts and to indicate what will appear if the clicks the button. A useful set of free calendar icons can be found in the Iconic icon set, available under the Creative Commons Attribution-ShareAlike license. One of the Iconic calendar icons is shown in the demo above.
This control was the subject of a user interface blog post.