Palantirs, the death of Saruman, and the ride to Gondor
Merry, Squire of Gondor, Dernhelm, and the Ride of the Rohirrim
Paths of the Dead and the Corsairs of Umbar
Introduction to Minas Tirith and Denethor, Pippin of the Guard
Wounding of Faramir, the siege, the breaking of the gates, Denethor's suicide
Death of the Witch King and the battle of the Pelennor
March on the black gates
Shelob and the escape from Cirith Ungol
Frodo and Sam disguised as orcs
The destruction of the Ring
The crowning and wedding of Aragorn
Wrap up and the Grey Havens
Wow. THAT'S a movie!
In the book, ROTK is actually fairly short once you take out the appendices. If you chop most of everything after the wedding...it's manageable. Even if you add in the confrontation with Saruman, the palantir, and Shelob.
It is unclear what they will do in regards to Saruman's fate. They may leave it unaddressed.
I suspect one reason that Shelob was moved back to ROTK is that there's a real imbalance in storyline in the third book between Frodo/Sam and the rest of the Fellowship. Especially if "Flotsam and Jetsam," "The Voice of Saruman," and "The Palantir" (three full chapters) are all being moved in some form to the third movie.
I don't object so much to such adjustments given that Tolkien himself was displeased with the idea of publishing his work in three volumes. In the end, both the movies and the books must be judged in totality.