Since I've been mentioning sermons from Pastor John Piper lately, I just wanted to mention that the http://www.desiringgod.org/ is a wonderful resource and has been a huge blessing to me. I like to listen to sermons while working on other things. Then when I have more time, I can go to the website later and actually read the manuscript to delve into the material more deeply. The quotes I have used below have been cut and pasted from manuscripts of his sermons. The Desiring God website is an awesome resource, and I highly recommend it!