A-ha - "Take On Me" (partially found instrumental demo of song; 1983)
A-ha is a Norwegian Synth-pop trio who you might recognize as the creators of "Take On Me". Some of their other hits include "The Sun Always Shines On T.V." "Cry Wolf" "The Living Daylights" The band was formed in 1982 and is still around despite splitting up in 2010. The band has 10 albums and is one of the most successful Norwegian bands. They've had 2 Guinness World Records for the largest rock concert attendance and longest held high note live, which is 20.2 seconds.
Their most famous song, "Take On Me" was originally known to have 4 different versions before the song we all know today, all of the earlier versions have been released on either a single or box set excluding one which has been found. However, there is a Norwegian documentary from 2005 which has a clip in it with this lost demo. There is an instrumental demo in the documentary which has never had a proper release other than this small bit.