Good Omens is the story of a demon who didn't so much fall as saunter vaguely downward, and an angel who was just enough of a bastard to be worth liking, and how they fell in love and attempted to save the world and realized that they could just pick a third side to both be on.

I think there was a TV show or something recently? (Just kidding, I did actually watch the show for this one.) So there's a lot of fanfic from the show. But I've been in this fandom since 1998 - I had a sleepover at shinyhappygoth's house, and read her copy of the book instead of sleeping (we had wild sleepovers, clearly). And the first online slash fic I ever read was Crowley/Aziraphale! And also there's too much show fic, I can't narrow it down, so have some classics of old bookfandom.

• And when he falls (1234 words) by torch
  Fandom: Good Omens - Neil Gaiman & Terry Pratchett
  Rating: Mature
  Warnings: No Archive Warnings Apply
  Relationships: Aziraphale/Crowley
  Summary:

  There are many ways to celebrate having avoided the apocalypse.




• The Sacred and the Profane (35477 words) by afrai
  Chapters: 15/15
  Fandom: Good Omens - Neil Gaiman & Terry Pratchett, Good Omens (TV)
  Rating: Teen And Up Audiences
  Warnings: Creator Chose Not To Use Archive Warnings
  Relationships: Aziraphale/Crowley (Good Omens)
  Additional Tags: Alternate Universe, Angel Crowley (Good Omens), Demon Aziraphale (Good Omens)
  Series: Part 1 of The Sacred and the Profane universe
  Summary:

  Somewhere else, the happy ending was different.




• Ordinary People (The Anything But Ordinary Remix) (14447 words) by cimorene
  Fandom: Good Omens
  Rating: Mature
  Warnings: No Archive Warnings Apply
  Relationships: Aziraphale/Crowley
  Additional Tags: Remix, Romance, First Time, Alcohol, Wings, Humor, Making an Effort (Good Omens), Canon - Book, Getting Together
  Summary:

  Crowley has started to take a proprietary interest in Aziraphale's bookshop.