Not an expert but "I Am Shelby Lynne" is a must have
The various volumes of Country Got Soul are all good and provide a nice overview of a lot of artists worth delving into in their own right like Eddie Hinton and Dan Penn.
All the first four or five Bobbie Gentry albums are worth having
Sammi Smith's "Help Me Make It Through The Night"
EDIT ...
Tift Merritt is wonderful
Louvin Brothers for some of the roots of Gram Parsons