This is the Hour

From Halopedia, the Halo Wiki

This is the Hour is a song included in the Halo 3: Original Soundtrack. It is one of the most recognizable themes in the entire game. A variation of this song is heard in the Halo 3 E3 video. It follows the song, Finish the Fight.

The song plays during the ending cutscene of The Storm.

The very beginning is mainly choir, followed by the well-known piano motif. This is then repeated by the entire orchestra. The song swells to a dramatic climax, then abruptly stops.

It runs for 2:06.

Halo Original Soundtracks (Source)
Halo: CE Original Soundtrack	Opening Suite • Truth and Reconciliation Suite • Brothers in Arms • Enough Dead Heroes • Perilous Journey • A Walk in the Woods • Ambient Wonder • The Gun Pointed at the Head of the Universe • Trace Amounts • Under Cover of Night • What Once was Lost • Lament for Pvt. Jenkins • Devils... Monsters... • Covenant Dance • Alien Corridors • Rock Anthem for Saving the World • The Maw • Drumrun • On a Pale Horse • Perchance to Dream • Library Suite • The Long Run • Suite Autumn • Shadows • Dust and Echoes • Halo Theme • Siege of Madrigal
Halo 2 Original Soundtrack Volume 1	Mjolnir Mix • Blow Me Away • Peril • Ghosts of Reach • 1st Movement of The Odyssey • Heretic, Hero • Flawed Legacy • Impend • Never Surrender • Ancient Machine • 2nd Movement of The Odyssey • In Amber Clad • The Last Spartan • Orbit of Glass • 3rd Movement of The Odyssey • Heavy Price Paid • Earth City • High Charity • 4th Movement of The Odyssey • Remembrance • Connected
Halo 2 Original Soundtrack Volume 2	Cairo Suite • Mombasa Suite • Unyielding • Mausoleum Suite • Unforgotten • Delta Halo Suite • Sacred Icon Suite • Reclaimer • High Charity Suite
Halo 3 Original Soundtrack	Luck • Released • Infiltrate • Honorable Intentions • Last of the Brave • Brutes • Out of Shadow • To Kill a Demon • This is Our Land • This is the Hour • Dread Intrusion • Follow Our Brothers • Farthest Outpost • Behold a Pale Horse • Edge Closer • Three Gates • Black Tower • One Final Effort • Gravemind • No More Dead Heroes • Keep What You Steal • Halo Reborn • Greatest Journey • Tribute • Roll Call • Wake Me When You Need Me • Legend • Choose Wisely • Movement • Never Forget • Finish The Fight • LvUrFR3NZ
Halo 3: ODST Original Soundtrack	Overture • The Rookie • More Than His Share • Deference for Darkness • The Menagerie • Asphalt and Ablution • Traffic Jam • Neon Night • The Office of Naval Intelligence • Bits and Pieces • Skyline • No Stone Unturned • One Way Ride • The Light at the End • Data Hive • Special Delivery • Finale
Halo Wars Original Soundtrack	Spirit of Fire • Bad Here Day • Perspective • Money or Meteors • Flollo • Just Ad Nauseum • Unusually Quiet • Flip and Sizzle • Put the Lady Down • Six-Armed Robbing Suit • Action Figure Hands • Status Quo Show • Part of the Plan • Work Burns and Runaway Grunts • Freaked Out • Rescued Or Not • Best Guess At Best • One Problem At A Time • De Facto The Matter • Part of The Problem • Out of There Alive • Through Your Hoops • Under Your Hurdles • Insignificantia
Halo Wars Original Soundtrack DVD exclusive tracks	X-06 • Fingerprints Are Broken • Five Long Years • Nothing Ventured, Nothing Gained • Quite the Vacation Resort • We're Burning Sunshine