D&D 5e Content Reference
Select which books to use:
The corebook, which contains all of the base content.
A short online supplement. Contains races and spells.
Contains subraces, subclasses, backgrounds, and a couple of cantrips.
Contains additional races, including monster races.
Contains subclasses, spells, racial feats.
Contains the gith race and various subraces.
A MtG crossover book. Contains races and subclasses.
The Tortle Package contains the tortle race. Adventure Modules sometimes contain usable content.
Has player character options that require DM approval.
Contains the various races of Eberron, and dragonmarks. UA material.
Not a rulebook, but playtest material found on the Wizards of the Coast website. See the bottom of the page for a list of Unearthed Arcana content.
Includes popular unofficial content such as the Blood Hunter.