Beethoven, Mozart, Bach, Schubert, Haydn (that order and then in no order)
Richard Strauss, Mahler, Bruckner, Buxtehude, Wagner, Sweelinck, Ravel, Schoenberg, Scriabin, Shostakovich, Ralph Vaughan Williams, Prokofiev, Purcell, Schumann, Rachmaninov, Brahms...
I like everything I guess, with the exception of most of the music from the last 70 years or so, and many of the "twelve-tone" composers.