Gossip Girl is based on the teen book series of the same name, written by Cecily von Ziegesar. The first book in the series was published in 2002.
Pretty Little Liars
Also based on a teen book series is Pretty Little Liars, by Sara Shepard, with the first book in the series published in 2006.
House of Cards
House of Cards is based on the trilogy of novels by Michael Dobbs. The first book in the series was published in 1989, also titled 'House of Cards.'
Orange is the New Black
The Netflix series is based on Piper Kerman's memoir, 'Orange is the New Black: My Year in a Women's Prison,' which was published in 2010.
Outlander is based on the series of novels of the same name by Diana Gabaldon, with the first book published in 1991. The series contains eight (yes, eight!) books.
Sleepy Hollow is a modern version of Washington Irving's classic short story, "The Legend of Sleepy Hollow," which was published in 1820.