Vampire: The Requiem has a fair amount of sourcebooks:
The original Requiem corebook is where it all begins, introducing the world of the Kindred and how to play one. It requires the World of Darkness core rulebook to play.
The covenant books (Carthians, Circle of the Crone, Invictus, Lancea Sanctum, Ordo Dracul, Belial's Brood) go in-depth into the large-scale social groups the Kindred have formed.
VII provides multiple options for the mysterious group of Kindred who hunt their own kind.
Rites of the Dragon is Dracula's account of his Requiem and the founding of the Ordo Dracul.
Kiss of the Damned is the Clanbook of the Daeva which, besides giving a closer look at the Succubi, gives some tips on how to handle more mature topics - more specifically, sex.
Savage and Macabre covers the Gangrel and presents a new (optional) mechanic for the Savages: The Red Surrender, a state of conciousness which boosts some characteristcs by relinquishing their grip on the Beast.
Shadows in the Dark focuses on the Mekhet. It also introduces an alternate form of Embrace: the Post-Mortem Embrace (allowing the Shadows to embrace corpses) and fleshes out the Shadow Cults, conspirancies and cults that influence the world in secrecy.
The Beast that Haunts the Blood elaborates the Nosferatu and guides us on how to create Necropoli, underground structures in which the Haunts dwell.
Lords over the Damned details the Ventrue and describes Malkavia, a supernatural plague/magic curse which intensifies the vampire's insanity while providing a new Discipline: Dementation.
Ghouls is about the blood slaves of the vampires and how they live their tragic lives. It also introduces Ghoul Families and Mandragora (ghouled plants).
The Bloodlines trilogy (The Chosen, The Hidden, The Legendary) covers more varieties of bloodline.
The Ancient duology (Ancient Mysteries, Ancient Bloodlines) covers the past of vampire society and the vampire "race", as well as what happens to a vampire as it ages.
The Night Horrors books specifically written for the Vampire line cover strange new forms of vampire (Wicked Dead) and particularly infamous and/or ancient vampires (Immortal Sinners).
City of the Damned: New Orleans covers the World of Darkness's version of The Big Easy, particularly how it looks through the eyes of the vampires who claim it for their own. It shouldn't be confused with...
Damnation City, which is about designing cities in the World of Darkness and how vampires can rule them.
The Blood is the Player's Guide to Vampire: The Requiem.
Nomads looks at Kindred who take up a nomadic lifestyle.
Coteries looks at how and why groups of vampires get together.
The Requiem Chronicler's Guide is a toolbox for building various types of chronicle.
The Danse Macabre takes the toolbox to the next level, ranging from personal to global, and providing an array of new rules.
Mythologies covers stories told amongst the undead about their possible origins, unique abilities and creatures that go bump in the night.
Requiem for Rome and Fall of the Camarilla are a duology describing the last major vampire organisation and how it all fell apart during the collapse of the Roman Empire.
Invite Only covers how to build Kindred social interactions and gatherings.
New Wave Requiem is a historical supplement for the 1980s.
The Testament of Longinus is a defictionalized version of the Lancea Sanctum's holy book.
Blood Sorcery delves into the secrets of Kindred blood magic.
Strange, Dead Love is a guide to modifying the game for paranormal romance.
Vampire Translation Guide is a quick and dirty guide to converting between Requiem and Masquerade.
Blood and Smoke: The Strix Chronicle is basically Requiem second edition, an all-in-one core PDF rulebook with everything necessary to start a game, no other books required. It overhauls the rules and setting, bringing the mechanics in line with the rules update of The God-Machine Chronicle.