Although it was originally recorded in 1974, there are pieces on Fred Frith's landmark Guitar Solos album that are probably still making guitar players scratch their heads wondering "How did he do that?" Don't expect any kind of Yngwie Malmsteen-style wankage; Frith instead uses a volume pedal, tapping, and other extended techniques to produce everything from chiming, bell-like notes to unearthly howls. It almost never sounds like standard guitar-with-plectrum playing, but the pieces have a logic (and beauty, in some cases) all their own.
This is free improvised, challenging, avant-garde music, but that doesn't mean it's unapproachable. Guitar Solos' lasting legacy is that it radically redefined the way some people think about the guitar.