Altering Frodo leaving the Shire (both in time and manor)
Faramir taking the Ring-bearer to Osgiliath
Denethor without a Palantír
The Witch-King breaks Gandalf the White's staff
The Dead coming to Minas Tirith
Éowyn hearing Théoden's last words instead of Merry
Frodo entering Shelob's lair without Sam
Aragorn beheading the Mouth of Sauron
Removal of the Scouring of the Shire