Teddy P.

It wasn't the car accident in 1982 that killed Teddy Pendergrass. But his career was never the same. He still made records afterwards, but they were smooth Soul. Pre-accident Teddy's records had an underlying fire that was missing in most of the other Soul singers of his era. He was indeed the prototype for the future R. Kelly's and Usher's.
For his solo career go with the TP album, probably the best Old School album by a male singer. It has great duets with Stephanie Mills and his best solo single, "Love TKO". After that go with any of his many compilations. Than dig deeper into his pre-accident catalog. For post-accident the best choice is 1986's Workin' It Back.
For Harold Melvin go to Itunes to download the many albums that aren't available on CD.