Siege of Madrigal

Halo 1
In the Halo: Combat Evolved level Assault on the Control Room, there are a couple places where you can stand and hear a song from Myth, another Bungie game, called the Siege of Madrigal. One can be found on the pyramid structure at the end of the level. There are three brackets on the large tower, get a Banshee and land on the second one. Facing the cliff, go to the right side of the bracket and wait a few seconds. If you can't hear it, walk around a bit to find the right place.

The other one can be found in the beginning of the level. You could ride on a Pelican, but you would most likely die. The best way to get to there is by grabbing a banshee, then returning to the start. It would be easier if you have another Spartan playing with you.

The Siege of Madrigal is also featured after the last track on the Halo Soundtrack CD.

Halo 2
You can also hear it on Ivory Tower in Halo 2. If you stand near the silver door, near the elevators, it will play. It plays Siege of Madrigal, or other sounds.

Halo 3
The Siege of Madrigal can also be found in Halo 3 on The Covenant. In the final stretch of the level, after defeating the Scarabs, ignore the waypoint and fly toward the Grey structure on the left (if looked at directly) that encompasses the building Truth is in. Carefully land the Hornet there (the return is possible without it, just much harder given the fall damage) and run along this ledge. Eventually, it will turn into a 45 degree slope; at the top, the song can be heard.

Warning: If you land on the building where Truth is, there is a possibility of activating the Revelation chapter prior to entering the building (The word will appear in the corner of the screen but nothing will happen). Should that happen (though to hear the song, you needn't go near the building itself) you will be able to continue the level normally until the point where the Flood forms ask to protect you and no further. The game will be stuck in the 'chapter title' mode with black bars across the screen and will not return control to you.