Cowboy Kisser

“Let me tell you how much I’ve come to hate you since I’ve began to live„

a familiar face

comics

required reading: lab rat and there are a couple of other, shorter official comics

turret lullaby

randolph the red-nosed turret (preserved on portalwiki)

videos

thinkwithportals.com has most of the ad shorts in one place, but not included there are

portal is free

aperture science romance safety compliance guide

perpetual testing initiative

audio

the portal 2 soundtrack is free online!

glados and cave johnson both have dota2 announcer packs

"don't say goodbye" is an unused glados song that ellen mclain WROTE

apocrypha

aperture desk job is free on steam

portal 2: the final hours is $2 and worth it

significant appearances in both poker night 2 and lego dimensions (including another glados song)

the portal ARG and potatofoolsday ARG

concept art!! (rip portal 2 art book, I will never be over you)

AND you can't forget the old aperturescience.com (archived by valve, thank god) you can look up commands to navigate it but I'd start by trying "help"

cave had cut lines too, many of which got recycled into lego dimensions, and the conversation with glados is a clear predecessor to his fate in desk job

and wheatley has some cut/alternate stuff, plus his tf2 cameo as the ap-sap