The Beatles - watched and enjoyed the "Yellow Submarine" cartoon as a kid and even got to be Maxwell in a performance of the song "Maxwell's Silver Hammer" at my local art camp (which in retrospect is a strange concept when dealing with elementary school age kids). But then during freshman year of high school a punk rock chick gave me her copy of "Sgt. Pepper" because "it wasn't punk enough" and I was instantly a lifelong fan.
Captain Beefheart - No work of art has ever meant more to me than "Trout Mask Replica". It's difficult to find a more rabid cult following than the one surrounding that particular Beefheart album. My experience with it is typical of most members of said cult- I listened once and was confused and somewhat repelled but intrigued at the same time by the sheer strangeness of what I was hearing. Some of the more "accessible" tracks like "Moonlight On Vermont" and "Ella Guru" made me suspect that there was something here worth pursuing. With each subsequent listen, the shifting angular rhythms, "ugly" tones and bellowing voice spewing surrealistic imagery sounded better and made more sense and what first seemed like a mess of disparate musical ideas crammed together began to reveal itself as a meticulously organized and arranged vision, a completely new approach. Soon I was listening to the album in full at least once a week. This lasted years. It's worth noting, however, that part of what made me stick with "Trout Mask" was discovering the far more accessible debut album "Safe As Milk" (which John Lennon referred to as his favorite album ever). However you acclimate yourself to The Captain's world, once you're there, you won't be coming back and your smile will be stuck.
Jimi Hendrix - Along w/ the aforementioned copy of "Sgt Pepper" given to me by the punk rock chick, my dad's copy of "Are You Experienced?" was the first classic rock album I heard in full. And in retrospect, they were the perfect 2 albums to start with- both kicked off/defined The Summer of Love and were released less than a month apart. Anyway, I was still a drummer at the time and loved Mitch Mitchell in addition to being awed by Hendrix (and this has only intensified: If one defines their favorite musician as the person whose playing moves them like no one else's, let it be said that Jimi Hendrix is my favorite musician) so it was the main album I drummed along to, along with "Trout Mask" and "Live At Leeds".
Skip James- the "Ghost World" movie. I'm sure I'm not alone there.
Spike Jones- via my parents, specifically a VHS copy of his "Musical Wreck-We-Um" show, which was hilarious. Wish I still had that. Not someone I can listen to too often (gotta be in a goofy mood) but still an all time favorite.
Moondog- the "Big Lebowski" soundtrack. I'm sure I'm not alone there either.
Django Reinhardt- "Sweet & Lowdown"- on a good day, my favorite film by my favorite director
Lastly, the Ken Burns "Jazz" documentary series and companion CD compilation series turned me onto quite a few of my favorite jazz artists, including Louis Armstrong, Sidney Bechet, Clifford Brown, Duke Ellington, Billie Holiday, Thelonious Monk, Sonny Rollins, Teddy Wilson and Lester Young.