The Revelation of the Ringwraiths

The Revelation of the Ringwraiths is a poem written by Philippa Boyens (Peter Jackson's wife and screenplay assistant) which was used as the lyrics to the Ringwraiths' theme in Howard Shore's music of The Lord of the Rings: The Fellowship of the Ring. Portions of the text are heard in five tracks out of the Original Motion Picture Soundtrack: "The Shadow of the Past", "The Black Rider", "At the Sign of the Prancing Pony", "A Knife in the Dark", and "Flight to the Ford".

Words
The Adûnaic words, which David Salo had translated from the English poem, are sung operatically by men of The London Voices in the soundtrack.

 Nêbâbîtham Magânanê Nêtabdam dâur-ad Nêpâm nêd abârat-aglar îdô Nidir nênâkham Bârî’n Katharâd

Translation
 We renounce our Maker. We cleave to the darkness. We take unto ourselves the power and glory. Behold! We are the Nine, The Lords of Unending Life.

A different translation is speculated at SoundtrackLyrics.com:  We refused our creator We went towards darkness We were handed strength and glory, Now Sauron we approach Lords of All lands'