The Expanse. The original novels were based on the authors' home game. No idea what system they used. It has come full circle with the RPG based on the books.
Record of Lodoss War. The franchise was based on the creators' home D&D game.
Over the Edge. Has one wild and crazy book, Pierced Heart by Robin Laws.
Games Workshop. They have lots of lines and lots of tie-in fiction. Blood Bowl, Warhammer, 40k, etc.
Changeling: The Dreaming. There are four books out for that game. Still haven't finished them, but they're good so far.
Paranoia. There are a few books for the game. No idea on the quality, but they are on my track down and read list.