Plan My Day - A planning tool which imports entries from the calendar and todo applications. - http://plan-my-day.sourceforge.net/
DateBk5 - Replaces the built-in Todo and Datebook applications on the Palm Organizer with an integrated program that maintains the general look and feel of the original applications. - http://www.pimlicosoftware.com/
Action Names - Enhances the built-in calendar and to do list with a series of advanced views designed to make managing your schedule easier. - http://www.iambic.com/pilot/actionnames/