Here's the quick answer I posted to DroidForums.org:
Hop on your PC and go to Google Calendar -> Settings -> Calendar Settings -> choose "Calendars" tab -> Browse Interesting Calendars (halfway down the page) -> choose "Sports" tab.
You now have access to Pro/College football, baseball, hockey, cricket, etc.
Once you subscribe to a sports calendar (international holiday, moon cycle, sunrise/set calendars are available, too) you can pick which are displayed on your phone through whichever app/widget you use.
