Vampire 30-Day Challenge : Favorite McGuffin
Clearly this would be the Book of Nod. Vampire was rich in its mythology, and in my games the Book of Nod was a delicious artifact to have in the game itself for players to learn about, fight over, struggle to keep or destroy, and have present as a key point in a story arc or two. The Book of Nod supposedly was penned to contain the very thoughts and words of Caine himself as he spoke of his experiences and visions. It was like, the vampiric Bible so to speak.
I feel bad, however, that the actual Book of Nod published by White Wolf wasn't that intense. Neither was the other companion piece, The Erciyes Fragments. Both, while very nicely written, had far too many art pieces that were clearly of the modern slant. A better approach to the book was how they did The Chronicles of the Black Labyrinth for werewolf which was written with lots of dark lore, and illustrated to look like those old wood-cut artwork as well.
I liked though the Book of Nod as a concept and I loved sharing players fragments of the actual passages in the book as we played. Back then, players weren't quite clear how many Antedeluvians really existed, nor what Clans and Bloodlines existed during the Second City and so on. So to share passages from the book felt awesome for the players. It was a sense of discovery that sadly will be hard to repeat now in a time when a quick Google Search can reveal so much material that used to be stuff that was fun to learn in-game.