I was heavily influenced by John Piper during my college years. Who wasn't? The first Piper book I read was "The Pleasures of God." My view of God was small before that book.
At the beginning of this semester, my preaching professor (& dean - Dr. Moore) asked the class to introduce ourselves and name one very influential sermon. I was struck by how many people mentioned sermons by John Piper. If you have listened to much of Piper, I am sure you can recall a sermon where the Spirit moved your heart to love Christ more and love sin less. If you have never heard Piper, peep this.
Justin Taylor has a great post celebrating Piper's 30th year at Bethlehem by recalling how God called him there. Check it out.