How to find Borderlands 2's quirkiest easter eggs

Update: A new video has come about that shows off the Dark Souls easter egg, so you don't have to find it. Because in true Dark Souls form, it looks like a pain to get to.
Borderlands 2 - Dark Souls Easter Egg Watch on YouTubeOriginal Story: The internet seems positively atwitter about Borderlands 2 on its European release day and the fine folks at Gamefront have showed us how to make the most of Gearbox's open-world shooter by detailing how to unlock several of its niftiest easter eggs.
The first is a Minecraft-themed area that comes complete with breakable cubes and culminates in low-def block heads for the various classes.
Borderlands 2 - Easter Egg - Secret Minecraft Area and Minecraft Skins Watch on YouTubeThe second unlocks the "What does it mean" achievement inspired by the double rainbow internet sensation. Near the Hyperion base you can discover an audio log of antagonist Handsome Jack losing his s*** over a double rainbow. Claptrap does the same.
Borderlands 2 - Easter Egg - Double Rainbow All the Way (Secret Achievement) Watch on YouTubeThere are plenty of other cute references in sidequests, but they're either very minor or not quite obscure enough that you won't find them on your own, so why ruin it?
Our Christian Donlan awarded Borderlands 2 a 9/10 and called it "a hillbilly moonshiner sort of game," but noted it was like "the hillbilly made majestic" in his review.