Sources for the things we have added:

http://www.gnu.org/graphics/gnu-and-penguin-color-1024x946.png (GFDL/GPLv2+)
http://www.gnu.org/music/free-software-song.ogg  (No copyrights asserted)
http://www.gnu.org/licenses/gpl.txt  (renamed GPLv2.TXT) (Free redistribution)
http://www.gnu.org/philosophy/fsfs/rms-essays.pdf (Free redistribution)

A talk I'm going to give:
ForkingUbuntu.odp
This is distributed under the GFDL (without invariant sections)