2001 uses works by several classical composers. It features music by
Aram Khachaturian (from the Gayaneh ballet suite) and famously used
Johann Strauss II's best known waltz, On The Beautiful Blue Danube,
during the spectacular space-station rendezvous and lunar landing
sequences. 2001 is especially remembered for its use of the opening
from Richard Strauss's Also sprach Zarathustra (or "Thus spoke
Zarathustra" in English), which has become inextricably associated with
the film and its imagery and themes. The film's soundtrack also did
much to introduce the modern classical composer György Ligeti to a
wider public, using extracts from his Requiem, Atmospheres, Lux Aeterna
and (in an altered form) Aventures.

http://en.wikipedia.org/wiki/2001:_A...8film%29#Music