Kraftwerk song from 1978(listen from around 1 minute in):
http://www.youtube.com/watch?v=VH0Js8qdnyA
Madonna - Ray of Light from 1998:
http://www.youtube.com/watch?v=a4tD8dy9Reg&ob=av3e
It was only until the 1990s that wavering pitch baselines became common.