Begin at http://missionalchurchnetwork.com/ Lots of foundational blogposts and links from there to many of the authors listed down below in the starter books post.
See the basic frequently asked questions about "The marks of missional church" at
http://thebolgblog.typepad.com/thebolgblog/2006/01/marks_of_a_miss.html by Ryan Bolger, now at http://www.ryanbolger.com/.
Also for a good place to use as a hub go to http://www.friendofmissional.org/ especially for the conversation about whether or not, or how, a "traditional" meaning modern-era church can become missional.
Also check out, especially the descriptions of the churches in the network over at,
Imagine connecting the insights here with the insights of the progressive Christian movement, http://www.uuchristian.org/ or http://www.tcpc.org/, or denominations on the cutting edge of theological engagement with pluralism in the 21st century.
For a Unitarian Universalist side of things, who works with different denominations, someone who gets it, check out the recent work of Michael Durall at http://www.vitalcongregations.com/