Public songbooks
Growing up with the Beatles, Stones, etc., and picking up the guitar as an adolescent, I felt incapable and unworthy of even attempting to play the songs of my heroes. As I grew older, I went back to the songs of my youth and was flabbergasted to see just how "playable" those "untouchable" songs really were. It also gave me an added appreciation of just how unique those artists really were. Now in my 50's, it amuses me to see how kids nowadays eat the Beatles, Stones, Hendrix, etc. up as if they were brand new. My latest interest involves browsing YouTube for "cover songs", especially ones by established bands covering other established bands. One good example: Red Hot Chili Peppers. Those guys have their own inimitable style, but some of their covers (I Get Around, Brandy, Castles Made of Sand) show me that they also appreciate and recognize a good song regardless of it's era.
Beatles, Tom Petty, R.E.M, Beach Boys, Lennon/McCartney, Little Feat, Led Zeppelin, Pink Floyd, Lovin' Spoonful, Looking Glass, Tom Petty & The Heartbreakers, Unknown...