1. Rachmaninov 3rd Concerto. As a kid I was accustomed to hearing Bach, Mozart, and Vivaldi around the house. Pleasant music all, but it didn't speak to me. I was studying the violin, but it felt like a formality; classical music was for other people. One day, when I was 8, my father sat me down by the stereo and said, "Listen." It was riveting, of course, and the shock changed my outlook: this music was for me after all. A couple years later I had started studying piano, and within a few years more I'd given up my various other instruments. Even now I can't listen to this concerto more than once or twice a year. In addition to its own ravishing beauty, it has so much personal meaning for me that the combination is emotionally overwhelming.
2. Medtner Sonata-Reminiscenza. I had been away from the piano for several years when I discovered this Medtner fellow and gradually became drawn to his music. When I finally decided it was time to start playing again, I looked for a piece that would be endlessly fascinating to work on. I loved listening to this sonata -- for me, it does everything that music can do -- and when I read Marc-André Hamelin's comment that he "needed it every day", I knew this was the piece I sought. A year and a half later, I know exactly what he means. On the occasions when I'm able to do it some justice, it's as close to a religious experience as anything I can imagine.
These two set the bar high, and for me nothing else comes close. Rachmaninov made me a musician; Medtner is making me a pianist and, with luck, a composer.