This is the song sung by Pippin (Billy Boyd) for Denethor. It's found on the Lord of the Rings: The Return of the King soundtrack, and is entitled The Steward of Gondor.

Home is behind
The world ahead
And there are many paths to tread
Through shadow
To the edge of night
Until the stars are all alight

Mist and shadow
Cloud and shape
Hope shall fail
All shall fade