Sleep: This is the vocal version of this song performed by Whitacre's Virtual Choir. The virtual choir is a live streaming group of people from around the world all singing together. What an amazing experience making music like this.
http://www.youtube.com/watch?v=6WhWDCw3Mng
Lux Arumque: This may be my favorite piece by him at the moment. This version is performed by the renowned Polyphony choral group.
http://www.youtube.com/watch?v=m1sYkJHipvg&safety_mode=true&persist_safety_mode=1
Equus: This song is an instrumental version. Its amazingness is evident just listen. Words can't describe.
http://www.youtube.com/watch?v=2ilQaKuWWBs
October: This song is slow and beautiful and brings about many different emotions. See how it makes you feel.
http://www.youtube.com/watch?v=gpV6PQLDqwY&safety_mode=true&persist_safety_mode=1