The following films are stand-alone and do not share continuities with each other or other films.
Superman: Doomsday (2007)
Justice League: The New Frontier (2008)
Wonder Woman (2009)
Green Lantern: First Flight (2009)
Batman: Under the Red Hood (2010)
Batman: Death in the Family (interactive short) (2020)
All-Star Superman (2011)
Green Lantern: Emerald Knights (2011)
Superman vs. The Elite (2012)
Superman: Unbound (2013)
Justice League: Gods and Monsters (2015)
Justice League: Gods and Monsters Chronicles (web series) (2015)
Batman: The Killing Joke (2016)
Batman: Gotham by Gaslight (2018)
Superman: Red Son (2020)
Batman: Soul of the Dragon (2021)
Injustice (2021)
Catwoman: Hunted (2022)
Batman and Superman: Battle of the Super Sons (2022)
Batman: The Doom That Came to Gotham (2023)
Watchmen (2024)
Superman/Batman
This continuity is based on the Superman/Batman storyline.
Superman/Batman: Public Enemies (2009)
Superman/Batman: Apocalypse (2010)
Justice League (JLA)
This continuity is based on JLA storylines published in 2000.
Justice League: Crisis on Two Earths (2010)
Justice League: Doom (2012)
Dark Knight Returns
This continuity is based on Frank Miller's Batman: Year One arc and The Dark Knight Returns.
Batman: Year One (2011)
DC Showcase: Catwoman (short film) (2011)
Batman: The Dark Knight Returns Pt. 1 (2012)
Batman: The Dark Knight Returns Pt. 2 (2013)
Other universes
Batman: Gotham Knight (set in the Nolanverse, although it is not necessarily considered canon) (2008)
Batman: Assault on Arkham (set in the Arkhamverse) (2014)