Tim Keller, Pastor of Redeemer Presbyterian Church,
has this good article regarding the importance of being missional.

http://www.redeemer2.com/resources/papers/missional.pdf

In his lectures regading the emerging chruch (www.christwaymedia.com), D. A. Carson recommends Tim Keller and Redeemer Presbyterian Church as a model for doing post-modern Christian work.  See also Keller's work on preaching in a post-modern city, part 1 and part 2.