Lords of Nal Hutta is my favorite "era" book. It really helps bring Hutt Space to life.
I'd love to see another criminal faction or organization get the same treatment: Crimson Dawn, Black Sun, Crymorah, the Pyke Syndicate, et cetera. (Or all of them, actually.)
How did the organization get its start? Who are the most important figures? What are their goals and motivations? Where do they have a presence within the galaxy? Are they expanding or in decline? What's life like within the organization and for those around them? What activities do they focus on? Who are their main rivals? How do they interact/conflict with the Empire and other criminal factions?
Think about what makes the Five Families, Sinaloa Cartel or Yakuza unique and compelling. Detailing similar organizations from the Star Wars universe could help create countless interesting campaigns.