The Lineages and Histories of the Great Houses and a certain dagger of interest.
The Lineage and Histories of the Great Houses of the Seven Kingdoms is a book detailling the history of the Great Houses of Westeros, including the lineage and appearance of all heirs, with illustrations of each house's individual sigil.
Season 1
Cripples, Bastards and Broken Things
Lord Jon Arryn asked Grand Maester Pycelle for the book shortly before his death. When hearing of his old mentor's interest in the tome, Eddard Stark borrows it from Pycelle as well.
A Golden Crown
After his daughters note that Crown Prince Joffrey has blonde hair, Lord Stark checks the Lineage and Histories, and discovers that all members of House Baratheon are described as "black of hair", except for the "golden headed" Joffrey, leading Ned to realise that he wasn't the real heir.