Free lectures from Covenant Seminary. Try these links:
Contextualizing Ministry 1, 2004
http://www.covenantseminary.edu/resource/Keller_Connect2004_Breakout1.mp3
Part 2
http://www.covenantseminary.edu/resource/Keller_Connect2004_Breakout1b.mp3
Also Preaching to Believers and Unbelievers
http://www.covenantseminary.edu/resource/Keller_JRW_FA04Lectures.mp3