You make it sound like Barber's Adagio was made for Homeworld. Also, I don't really like how they upped the tempo in Homeworld's version. It gimps the sorrow it's supposed to transmit.
http://www.youtube.com/watch?v=XS3NK0LKzbo
Of course I'm aware the soundtrack is a lot older than Homeworld, which is why I only posted it now. I wondered if it actually counted.
EDIT: I prefer the faster tempo. In terms of game themes with only a choir, I guess this one "counts" more. Chandelier - To All Things. Not as chilling as Adagio for Strings, unfortunately.