Anything by the Supremes, Smokey and the Miracles, Stevie Wonder (at least up until the 80's), Marvin Gaye, Sam Cooke. Really though, The Supremes are so underrated. I don't think they have a single song that is less than great.

Aretha Franklin's "I Never Loved a Man the Way I Love You" is one of the greatest R&B albums front to back at a time when R&B was more focused on singles than albums. Highly highly recommend that one.