Season 1, Episode 6: "House of the Rising Sun"
Season 1, Episode 8: "Confidence Man"
Season 3, Episode 15: "Left Behind"
Season 6, Episode 8: "Recon"
Billed as, "a timeless novel of exile, courage and survival," Watership Down by Richard Adams has made enough appearances in the past six seasons that one might argue it deserves an end credit. Lost and Watership Down both share the themes of exile, the search for home, a frightening smoke monster and the dominant idea that Jack proclaimed at the end of Season 2—"Live together, die alone."
We first see Sawyer reading Watership Down in Season 1, Episode 6, "House of the Rising Sun," when he chooses to stay at the beach instead of moving to the caves as Jack requests. In Season 1, Episode 8, "Confidence Man," Sawyer is accused of withholding Shannon's inhaler medicines and the book gives it credence, as it was in the same luggage. Sawyer says to Kate: "Helluva book. It's about bunnies."
The novel is seen again in Season 3, Episode 15, "Left Behind," when Hurley cons Sawyer into being nice to the other survivors by telling him that they will take a vote on whether or not he should be banished. Fast-forward to Season 6, and Watership Down is seen on Sawyer's dresser in his sideways reality. In the episode, Miles asks sideways Sawyer, "Do you want to die alone?"