What actions freeze time?

Via drop-test (dropping an item and seeing whether its fall stops), the following actions appear to pause time:

• opening the Character Menu or any of its submenus (even if you use Quick bindings to bypass the Character Menu)
  • Items / Inventory
  • Magic
  • Skills
  • Map
• opening any of the tabs of the System menu
  • Journal
  • General Stats
  • System
• any action which indirectly opens your invenory
  • trading
  • looting
  • pickpocketing
  • but not crafting
• opening your Favorites

The only things that stop time in Skyrim are opening an inventory menu or an interface menu. This does not include the various crafting menus, but includes buying, selling, and pickpocketing.