Here, I take ‚incest’ to mean mother/son, father/daughter and siblings (mostly full, only rarely half) relationships. Due to the universe(s) in which many of the works are set in, the half-siblings or adoptive siblings are often not counted as incest. Similarly, the stance varies on further relations.
Many of the fantasy works are based on Middle Ages – on plenty of real life examples and not on the strict canon law.
Note that the slash (homosexual) incest appears, which is almost unheard-of in history.
Another thing to remember: I mention books I have either read or I know much about them. I do not aim to reproduce the entire list from Wikipedia.
– Game of Thrones: Jaime/Cersei (twins), the Targaryens (siblings, after the manner of Ancient Egypt)
– Flowers in the Attic
– Dune: Leto II/Ghanima
– Paradise Lost: Satan/Sin
– Blue Bloods by Melissa de la Cruz
– Oedipus the King: Oedipus (Edyp)/Jocasta
– Wideacre Trilogy: Beatrice/Harry
– Children of Hurin or Silmarillion: Turin Turambar/Nienor Niniel
– Tigana: Dianora/Baerd
– Elenium: Aldreas/Arissa
– One Hundred Years in Solitude
– Harry Potter: Twincest (Fred/George or Padma/Parvati)
– Harry Potter: Weasleycest (Bill/Charlie, Ron/Ginny or others)
– Harry Potter: Blackcest (a variety of pairings including, but not limited to: the Black sisters in various combinations, Narcissa/Sirius, Andromeda/Sirius, Bellatrix/Sirius, Sirius/Regulus)
– Harry Potter: Pottercest (Lily Potter/Harry Potter, James/Harry; the name can also refer to Albus Severus/James or James Sirius/Lily Luna or Albus Severus/Lily Luna)
– Harry Potter: Malfoycest (Narcissa/Draco or Lucius/Draco)
– Lord of the Rings: Eomer/Eowyn, Elladan/Elrohir
– Star Wars: Luke/Leia and possibly Jacen/Jaina, Jacen/Anakin
– Baldur’s Gate: Imoen Romance mod