Normally I avoid tie-in fiction for RPGs. 90% of the time, you can what I call, "hear the dice being rolled in the background." Most of it tries to cleave too close to the rules and less interested in telling a good story.
But that is not always the case.
Back when I was gearing up to run the GDQ series for my family, I wanted to read what others had done, to immerse myself in the world and the adventures again. That is when I discovered the writing of Pauli Kidd.
Pauli took the familiar locations and then gave me characters I really enjoyed. The Justicar, Escalla, even Cinders. They were a very rare treat. She did a fantastic job here, and I never heard the dice once.
Set in the World of Greyhawk, these books are less about these fabled locations and more about the characters. I had so much fun with them that I included Evelyn, the Princess Escalla as the daughter of the Justicar and Escalla (half-human/half-pixie, looks like an elf) in my own running of these adventures. Through interaction with the party, she became the lead freedom fighter to free the surface elves from their enslavement by the Drow across multiple planes.
Another set are the Brimstone Angels series for the Forgotten Realms by Erin M. Evans. While the books focus on the twin tieflings Farideh and Havilar, the books cover some of the biggest events in Faerûn and even deftly cover things like the changes in world history from 3rd Edition to 4th Edition to 5th Edition.
Her books were so well received that it even added details to the rules, such as Mahen, Farideh, and Havilar to the list of Dragonborn names.
There are few others, but these are the best in my mind.
