Beach Boys
Everly Brothers
Crosty Stills, Nash Everly Brothers
Pointer Sisters (Rock?)
Friends of Distinction (Rock?)
Association
Poco
New Riders of the Purple Sage
are among my a few of my favorites
And then there is Motown (little mentioned on this site, wonder why, no Motown fans?)
Marvin Gaye and Tami Terrell
The Four Tops
Temptations
Supremes
Martha and the Vandellas
Earth Wind and Fire
I really don't care what the genre, I love listening to groups harmonize.