Google Calendar's gallery isn't back yet, but you can now subscribe to sport calendars for baseball, football, soccer, rugby, hockey and basketball. How to find the new calendar directory? Click on "add" below the list of "other calendars" and select "interesting calendars".

Like Gmail, Google Calendar is now a container for iGoogle gadgets. To enable gadgets, go to Google Calendar's settings page, select "Labs", click on "Enable" next to "Add any gadget by URL" and don't forget to click on "Save". You'll see a small box that lets you enter the URL of a gadget. It's not user-friendly and Google forgot to list some samples, but you can try this Wikipedia gadget:
http://www.google.com/ig/modules/wikipedia.xml
or this gadget for driving directions:
http://www.google.com/ig/modules/driving_directions.xml