LotR: RotK

[Arutha]

So what about the staff?

There, as far as I can tell, Jackson wasn't true to the book.

In the book, when the gates of the city are broken, the Witch-King is there, sending the defenders fleeing in terror.
But Gandalf stands and denies him entrance into the city (his second "you cannot pass" utterance ;) ).

The Nazgul don't take such an active role in the attack on the city. They're a weapon of terror, not destruction. In the book, the Nazgul fly high over the city, never coming bowshot range... or within the range of Gandalf's spells.
But their shrieks are enough to send terror within the minds of the defenders.

That also Gandalf counters, to some extent. Because we learn at the very end of the book that he is the wearer of the third elven ring of power.
Elrond wears the ring of Air. Galadriel wears the ring of water.

Gil-Galad, the last high king of the Elves wore the ring of fire. Gil-Galad fell against Sauron at the end of the Second Age. Cirdan, warden of the Grey Havens, then became the keeper of the ring of fire. But when the Istari (Gandalf, Saruman, Radagast, Pallando, Alatar) came to middle-earth upon Sauron's awakening, Cirdan entrusted Narya, the ring of fire, to Gandalf.
Narya is the ring of fire, but its special power is that it's the ring of hope. It rekindles the flame of hope in the hearts of the Free people. That's why Gandalf is ever the traveller, mustering people against Sauron, cleansing people's minds from his evil influence.

And that's also probably why of the five Istari, Gandalf is the only one who stayed true to his mission.
Saruman's fall is detailed in the book.
Radagast's is only briefly mentionned: he didn't betray his cause, but rather grew weary of it. He does help Gandalf a little (he's the one sending the Eagles twice - the butterfly is Radagast's messenger), but mostly keeps out of the fight. The other two Istari are not mentionned in the book, only in other Tolkien writings and we learn that the lure of power was too strong for them to resist.