Tim Keller is my favorite teacher and author. I started listening to his sermons in 2001. Back then, you could only get his sermons on cassette tapes and by ordering them from Redeemer. During 2003-2004 life was such that Tim Keller was the main teaching influence in my life. A mentor if you will. I never stopped ordering Keller’s sermons. Each year I would order just about every 2-3 weeks and as time went on, the format changed. From tapes to CD’s and finally to Mp3’s. My work commute times were actually my favorite. I would spend hours listening to Keller in my car or plugged into headphone on BART. I have listened to just about every series a few times, and several more than a dozen times. Because of Tim Keller I was able to connect my childhood/early teens raised on Theology to a very real and practical living out of what I knew in my head. I don’t know how to explain it other than he is able to engage my heart, mind, and bring me to Jesus in a way that just gets me every time. Repentance, change of lifestyle and habits, real and practical actions as a result of listening.
Books by Tim Keller
Tim Keller’s books, reading them is like having C.S. Lewis in my own time. His books do much the same for me as C.S. Lewis, but in a more relevant way. “Every Good Endeavor” gave me passion for life that I never had, and prompted me to stop living and working for my own desires. It also prompted me to brainstorm and create EmotionsManager. His book “Walking with God Through Pain And Suffering” was so incredible. I read it twice. Galatians For You and Judges For You were fun to read as well. Really, all of his books are well written and very informative.
Get a sermon
Keller’s sermons are hight quality. You should download a few. 
I had it in my head several times to take sermon notes and post them online. In 2010 I tried that, but was not consistent at all. (Update: attempting this again here.) Fun to look back at that site though. I hope to meet Tim someday and just shake his hand and tell him my story in a few minutes time, thank him for his faithfulness to the Gospel.