Theoden

Theoden: Simbelmyne. Ever has it grown on the tombs of my forebears. Now it shall cover the grave of my son. Alas, that these evil days should be mine. The young perish and the old linger. That I should live to see that last days of my house.
Gandalf: Théodred's death was not of your making.
Theoden: No parent should have to bury their child.

Theoden: Where is the horse and the rider? Where is the horn that was blowing? They have passed like rain on the mountain, like wind in the meadow. The days have gone down in the West behind the hills into shadow.
*The Two Towers*

Theoden:...Forth, and fear no darkness!Arise. Arise, Riders of Theoden. Spears shall be shaken, shields shall be splintered. A sword day... a red day... ere the sun rises.
[The King rides past his men, hitting their spears with his sword as he goes]
Theoden: Ride now... Ride now... Ride. Ride for ruin and the world's ending.
[He stops and prepares to face Sauron's army]
Theoden:Death.
Rohirrim:Death.
Theoden:Death.
Rohirrim:Death.
Theoden:DEATH.
Eowyn, Merry: Death.
Theoden: Forth, Eorlingas.
*Return of the King*
(sourced from imdb.com)

this is probably the two best quote from the entire Lord of the Rings trilogy...Theoden HAS to be the Best character in the entire Lord of the Rings trilogy if for nothing else but sheer quotability :)