Update (July 27 2007): As always with these Greasemonkey scripts, any minor change in a site's code can make the script stop working. The ToDo list described below doesn't work anymore, so you could try a similar one.
Google Personalized Homepage has a to-do gadget, who'd be be better suited in Google Calendar. As there's no option to add gadgets in Google Calendar, someone created an even simpler version as a Greasemonkey script.
While you can't add priorities, sort the events by date or change their order, it's handy to have a list of events next to the calendar. The ToDo list is saved in Google Calendar as fake events, so you'll be able to see it if you use other computers (you'll need to have Firefox + Greasemonkey, though).
How to add the ToDo list? First install Greasemonkey for Firefox, restart the browser and then install this script.