Gyorgy Ligeti:

Requiem For Soprano, Mezzo Soprano, Two Mixed Choirs & Orchestra [1963-65]

Lux Aeterna, for 16 solo voices [1966]

Atmospheres [1961]

Finally, the tracks everyone has been clamoring for: the scary-voices music from 2001.

This is a bit of a belated tribute to Gyorgy, who departed this solar system on June 12, 2006.

The next Ligeti piece I am excited to hear is:
Clocks and Clouds, for 12 female voices (1973)

Get some Ligeti on CD or vinyl.