Lord of the Rings theme?

when ever i look up "Lord of the Rings theme" i never get what i want. i always get some other theme. could someone tell me the name of the song that has the part of the theme that i think is the most recognizable in the lord of the rings. if you need clarification on that, i mean the part of the theme that plays when arogorn (in the third movie) says, "for Frodo" and charges the black gate.