Who are the greatest songwriter/performers of all time?  

I'm asking about the greatest songwriters who also successfully performed their material. So this eliminates names like Burt Bacharach or Oscar/Hammerstein, even though they wrote excellent songs. Elvis wrote some of his material, and he would be near the top of the list because he was such an excellent performer. On the other hand, Paul McCartney and John Lennon are near the top because they were so prolific and ingenious at writing, even though they rate no where near Elvis in performance.

So, here is my short list - the Beatles (McCartney-Lennon-Harrison), Led Zeppelin (Page-Plant), Sting, Steely Dan (Fagen-Becker), Kris Kristofferson, Gordon Lightfoot, Pink Floyd (Waters-Gilmore), John Denver, Dolly Parton, Merle Haggard, Vince Gil, Allison Kraus, Eric Clapton, James Taylor (and his ex-wife - name escapes me), Rush (Getty Lee), Ambrosia (don't know the names of the writers, but love their music), Supertramp (ditto), Fleetwood Mac (McVie, Nicks, Buckingham), Earl Thomas Conley, Willie Nelson, the Doobies, and Bob Wills.