First place to look is the Github repo.
https://github.com/KiCad/kicad-library

Others
https://github.com/octopart/CPL-KiCad-Library
http://www.kicadcloud.com/
http://kicadlib.org/
http://kicad.rohrbacher.net/quicklib.php
http://smisioto.no-ip.org/elettronica/kicad/kicad-en.htm
http://library.oshec.org/
http://gramlich.net/projects/pcb_footprints/index.html
http://cyclerecorder.org/footprintbuilder/
http://embeddedprogrammer.blogspot.in/2012/06/3d-and-footprint-libraries-for-kicad.html
http://www.jave.de/docs/kicad/image2module.html
http://projects.qi-hardware.com/index.php/p/xue/source/tree/master/modules