Never Forget is a song included in the Halo 3: Original Soundtrack. It is based heavily off of the Halo 2 song, Unforgotten - the beginning is almost exactly the same.
It starts with the Unforgotten theme played with strings, but four keys lower, giving it a more solemn mood. The motif is then repeated with choir. Choir then takes the melody, with a piano accompaniment. The song then swells to a definite upturn, switching to a major key. Almost immediately, it switches back to a minor key. Piano then takes the melody, playing more of the Unforgotten theme. The last minute of the song is exactly the same as Unforgotten.
It runs for 3:06.