Running From Home, by Donovan, the first time I heard alternating bass fingerstyle (early 1966). (I'd only been playing myself for one month at that time.)
That led me to Bert Jansch (who wrote it), and his version of Angie (better than Davy Graham's original)
Cliff's Romp, by Cliff Aungier (1966) - an obscure UK blues-ragtime player (known to Jimmy Page); first time I heard ragtime guitar (live), definitely blew me away, and led me to people I'd never heard of before like Big Bill Broonzy and Blind Blake. I
really wanted to play like that!
Cliff's Romp was never available on record, but it sounded a lot like this:
http://www.youtube.com/watch?v=Fm1qtX7Mz5w
(RIP Cliff...)
Then John Martyn and Stefan Grossman, late 60s. Martyn inventive and modern, Grossman painstaking revivalist, educational.
Then there was Django Reinhardt of course (first heard in the early 70s) - spoiled me for all other jazz guitarists.
It was a long time before an acoustic guitarist impressed me as much as those guys, not until Kelly Joe Phelps and Shine Eyed Mister Zen (his technique wasn't astonishingly better, but it was beautifully fluid).
Having stopped listening to Bert Jansch back in the late 60s, I was later amazed to hear this:
http://www.youtube.com/watch?v=J09ehzggVVo
(how does he do that on ONE guitar??? Took me a while to work it out...)
More recently, there's dozens of players, often using various tapping and percussive styles and open tunings, that are technically streets ahead of most of those 60s heroes (Jansch maybe excepted).
I saw this young guy recently:
http://www.youtube.com/watch?v=ZNGPs7F3AyI