Ozzy--My memory is fading, but I think the record that started the longer versions of songs was probably Bob Dylan's "Like a Rolling Stone". When it first was played on AM radio they only would play the first two verses (fitting barely into the usual 3 minute maximum), even though the single went for the full four verses/6 minutes. I remember one Saturday afternoon listening to Dan Ingram on WABC in NY (who was also an FM jock, with a jazz show), and in the last hour he was on he played the entire record. Shortly after that I started to hear the whole record played, though I think it may have been because about then I started listening to FM.
There were other long songs around that era--Cream's "Toad", the Doors' "Light My Fire" (FM version), "The End", "Soft Parade", etc., Serpent Power's "Endless Tunnel" (any of you actually remember that one?), and a lot more--as well as Iron Butterfly, so I guess I don't really think of them as starting the genre.
