Major changes are listed below (spoiler warning):
a) Some extra dialog in Merry and Pippin's first scene at Isengard, making them seem a little "stoned" from the pipe-weed.
b) A final confrontation between Gandalf and Saruman has been restored, including the final fates of Saruman and Grima Wormtongue and a slightly different acquisition of the Palantir.
c) The celebration at Edoras has a few extra little snippets, most notably a drinking game between Legolas and Gimli.
d) Right before Pippin takes the Palantir, Aragorn enters the Great Hall and has a conversation with Eowyn about a dream she had.
e) Extra dialog from Merry when Gandalf and Pippin leave.
f) An extra line of dialog when Pippin meets Denethor.
g) After Gandalf storms out of the White Tower, he has a long monologue explaining the history of Gondor to Pippin.
h) A new scene with Frodo, Sam and Gollum centered on the discovery of a ruined and defaced statue at the crossroads.
i) When Pippin and Gandalf are talking on the balcony, an alternate take is used in which Gandalf chokes on the smoke from his pipe.
j) After Frodo and Sam begin climbing the stairs, Sam warns and threatens Gollum not to betray them.
k) Additional footage when the Orcs cross the river showing they take the Gondorians by surprise.
l) More dialog from Faramir and more violence as well.
m) A scene in which Merry asks to serve Theoden and Gimli and Legolas wonder what is happening in Gimli's home.
n) After Faramir arrives in Gondor, there is a scene where Denethor confronts him for not taking the Ring, which includes an appearance by Boromir.
o) An additional scene between Pippin and Faramir before the former swears fealty to Denethor.
p) Additional dialog when Faramir is riding out of Gondor.
q) Additional lines from Eomer after he tells Eowyn not to encourage Merry.
r) An additional line of dialog when Aragorn says farewell to Eowyn.
s) More dialog from Legolas when he explains the Paths of the Dead. The Paths of the Dead sequence is heavily revised, including the appearance of thousands of skulls, wispy ghosts, an earthquake and Aragorn's emergence from the mountain.
t) We see Gothmog dismounting a warg as the siege of Gondor begins; additional action during the siege of Gondor, including the Orcs using a small battering ram on the gates and cheering on the approach of the huge battering ram, Grond.
u) A new scene in which Aragorn attacks the Corsair ships, which includes a cameo by Peter Jackson (he's the one killed by Legolas).
v) A scouting report is brought to Theoden on his way to Gondor; a conversation between Merry and Eowyn.
w) More footage as Denethor takes Faramir to be cremated alive.
x) As Gandalf is riding to rescue Faramir, he is attacked by the Witch King.
y) The charge of the Rohirrim is moved to after this scene.
z) Another line of dialog before Denethor lights his pyre.
aa) More action during the battle of the Pelennor, including a fight between Gothmog and Eowyn.
bb) After Eowyn kills the Witch King, Gothmog tries to finish her off.
cc) Pippin's search for Merry is much longer and he finds him at night.
dd) Eomer finds Eowyn on the field and mourns when he thinks she is dead. A restored healing sequence between Aragorn and Eowyn.
ee) A much longer fight among the Orcs in the tower of Cirith Ungol.
ff) After Sam rescues Frodo, we see a surviving Orc sneaking off with the Mithril shirt.
gg) Aragorn finds a Palantir in the White Tower and uses it to reveal himself to Sauron.
hh) Faramir and Eowyn meet in Minas Tirith after Aragorn leaves.
ii) Frodo and Sam, wearing a disguise of orc armor, are found and forced to march with a detachment of Orcs while trying to reach Mount Doom.
jj) Near Mt. Doom, Frodo and Sam throw away the last of their gear.
kk) While resting, Sam sees a star through the clouds.
ll) At the Black Gate, the Aragorn, Gandalf, Legolas, Gimli, Pippin, Merry, and Eomer are first confronted by the Mouth of Sauron. (This also induces a goof as his body & horse have disappeared when they retreat from the gate.)
mm) More dialog when Gollum (acting as Smeagol) attacks Frodo on Mt. Doom.
