Classic Rock: If you haven't already, turn on to The Beatles, Van Morrison, The Rolling Stones, Bob Dylan, and Neil Young.
As for pure guitarists, I enjoy a Brazilian guitarist named Bola Sete http://www.bolasete.com/
and a German named Ottmar Liebert.
Sitar music by Ravi Shankar and the more contemporary Ranjan Maharaj is excellent.
As for classical, name your mood, for me: Beethoven is the dark god, Mozart makes me feel studious, Debussey is devine, Bach supplies respite and religion, and Rachmaninoff ambition and courage.
Be sure to experience Jazz: Coltrane, Miles Davis, Charles Mingus, Louis Armstrong, Dizzie Gillespie, Charlie Parker.
Singers/songwriters: Paul Simon, Cat Stevens, James Taylor, Otis Redding, Eric Clapton, Jonie Mitchell
The Blues cannot be overlooked: BB King, Muddy Waters, Howlin' Wolf, Albert King, Buddy Guy, and Albert Collins
A good place to start with opera is Luciano Pavarotti
Enjoy and let us know what you think