The song you could be talking about is "Hey Jude" which was made by The Beatles. It ends in "Naaaa Naa Naa NaNaNa Naaa, NaNaNa Naaa, Hey Jude." Sorry if wrong song. <edit> Kylie Minogue's...
Well, there are several "La La" songs that come to mind: "If You Seek Amy," by Britney Spears starts out with "La Las" and repeats the same "La Las." Ashlee Simpson has a song called "La La." I guess...