Victimae paschali laudes is the Sequence chant for Easter Day. Charles Tournemire recorded an improvisation on the chant which was later transcribed be Maurice Duruflé. This transcription has become a popular piece of organ literature.
See a list of other popular chant themes here.
Videos:
Charles Tournemire (Philippe Lefebvre plays) – Victimae paschali laudes – Chartres Cathedral, France
Lorenzo Bonoldi – Versetti on Victimae Paschali Laudes – Basilica di San Carlo, Milano
Sergio Militello – Victimae paschali laudes
Daniel Roth with Eric Lebrun – Victimae paschali laudes – St. Sulpice, Paris, France