A newer version known as the DateTimePicker uses a text based calendar script (Look and feel is totally different). It is part of the component library available at http://myworkspace.sourceforge.net/
Krysalis Menu - drop down menu component. Available at Krysalis Also available from Tassel.
Tacos Library. Tacos provides high quality components for Tapestry, such as a Tree/DatePicker/ProgressBar/Autocomplete fields/etc.. It also provides a substantial amount of support for using ajax logic with tapestry and is quickly growing each day.