Matias Pelenur has created a GreaseMonkey script for adding a todo list into Google Calendar. This is pretty cool addon for extending Google Calendar to be a Google Organizer.
This is a prototype for a script to add a To-do list to Google Calendar. As of this writing it stores to-do entries in the GM local store, which means that each of your firefox installs/computers will have its own list.
Google Calendar Todo List – [Userscripts.org via Going My Way]