Reddy and Murray don't really belong in the same group with the others, ditto the Carpenters. On the Janis Ian, avoid the "best of" and go for 'Between the Lines' and 'Breaking Silence' instead. Add Armatrading's 'Me Myself I', Patti Smith's 'Horses', all three Karla Bonoff discs, and Kate Bush's 'Hounds of Love'. Joni Mitchell deserves a category of her own. "Blue" is a masterwork. "Hejira", "Hissing of Summer Lawns" and "For the Roses" all have strong material as well, tho less 'indispensable' than "Blue". If your CD player supports it, look for the HDCD remasters of the Joni discs. All of those artists are readily available used, fur hella cheap. Consider adding the Emmylou Harris (the "Best of" can work here) and Joan Baez' "Any Day Now", one of the best-ever sets of Dylan covers.