Steven Johnson is studio guest on Kurt Andersen's awesome Studio360 radio show, courtesy of WNYC. You can listen to Johnson and Andersen discuss emergent systems across cities, art & music, programming etc. Includes an interview with Brian Eno on emergent music, a commentary on the great urbanist Jane Jacobs, and remembers the late architect Samuel Mockbee. The show's kinda linear so you have to listen to some other discussion too, but it's all good [via Peter Marsh - thanks!]
Also found this interactive Java-based essay on emergence.