Tweak,
Love your threads, mister. Thanks for including our man, George J (even if he qualifies only as a singer), not to mention Beck, Cobain, Richard Thompson, and Lucinda Williams.
El Duce and Neil Diamond? You scamp, you. Too bad they never collaborated.
Among the giants not yet mentioned, I nominate Joni Mitchell, Randy Newman, and Chuck Berry.
Among the unheralded, how about Walter Salas-Humara of the Silos? I love this guy's work so much I "borrowed" his name as my moniker. Really, a great songwriter.
Two other unheraldeds knocking on the door: Brian Henneman of the Bottlerockets and Freedy Johnston.