These are three good overview talks and are suitable for getting a sense of how Keller's theology meets his missiology.
Gospel Renewal Here Keller, following Richard F. Lovelace gives an overview of his thinking on the need for spiritual revival or renewal. This gives one of many articulations of Keller's perspective on the church's problem (basing your justification on your sanctification, the problem of "religion") and the answer (an ever increasing appreciation and realization of salvation by grace). This lecture also includes a some material that is in the 2005-2006 MCM series that was free online for quite a while but is now available for purchase through the Redeemer Sermon Store. There's also a treatment of Jonathan Edward's teaching on Common Virtue vs. True Virtue.
Church and Culture: In this talk Keller gives a nice summary of some of the emphasis differences that are enflaming divisions within the church. He postulates that these arise from perspectives on the relationship of between church and culture.