How many music theory books written over 45 years ago are still taken seriously, never mind still in print?
It was my great pleasure to study with Leonard Meyer at the University of Pennsylvania from '86 through '89. Even though I am a composer and not really a theorist any more, I consider him one of my most influential teachers. His writings and lectures deeply affected me as a composer in that his understanding of music -- how it works, how it affects us, how our individual cognitive processes come to bear on what we are hearing -- found its way into my aesthetic. Even though Dr. Meyer in later years came to argue with himself (this was tremendous fun, by the way: sitting in his lectures, listening to him tell himself why his earlier writings were so wrong), this is great stuff, written by a great man.
Be forewarned that in spite of the title, this is musically technical stuff: don't expect vague, poetic philosophizing. The analyses are intense and detailed and require a strong background in music theory and form.