I know it isn't the best example of the Beach Boys harmonies (that would be Good Vibrations) but I never turn down a chance to post what I think is the best love song ever written. Plus the harmonies on the bridge as flawless.
The combination of Davey Johnstone, Nigel Olsson and the late Dee Murray gelled so incredibly well that Elton used them on virtually every track while they were all together in his band.
Ladysmith Black Mambazo were almost faultless in their harmonies and played a massive part in the worldwide success of Paul Simon's 'Graceland' album. Particularly when they were given most of the song, such as on 'Homeless'.