Iannis Xenakis - Not much more to be said. Someone gave me this album a long time ago as a gift. It's probably available elsewhere but I thought I'd share anyway. As far as I know these pieces aren't on CD. A great collection from a great composer.
Polla Ta Dhina for Children's Chorus and Orchestra (1962)
ST/10=1-080262 for Ten Instruments (1956-1962)
Akrata for 16 Wind Instruments (1964-1965)
Achorripsis for 21 Instruments (1956-1957)