This is an awesome sermon by Tim Keller on The Prodigal Sons:

http://download.redeemer.com/sermons/The_Prodigal_Sons.mp3

His new book The Prodigal God will be released October 30th.

My favorite quote from this sermon is:

"The reason you are so unhappy is because of your goodness. The main thing between us and God is not our sin as much as our damnable good works....Lay your deadly goodness down, down at Jesus' feet. Stand in Him and Him alone gloriously complete. We will never stop being older brothers until we see and are melted by what our true older brother did for us."