Gossip Girl
A full list of special holiday episodes

In the exclusive world of Manhattan's elite, the anonymous blogger Gossip Girl dishes the dirt on the scandalous lives of the city's privileged youth.
The show aired 1 Christmas episode, 4 Thanksgiving episodes, and 1 Valentine's Day episode.
Christmas episodes:

Season 1, Episode 11
Roman Holiday
Blair's dad arrives for the holidays with a surprise guest, while Jenny and Vanessa assist Serena in planning a memorable Christmas surprise for Dan.
Thanksgiving episodes:

Season 1, Episode 9
Blair Waldorf Must Pie!
Dan invites Serena and her family to celebrate Thanksgiving with his own family after discovering they would be spending it alone.

Season 2, Episode 11
The Magnificent Archibalds
Blair's Thanksgiving traditions are ruined by her mom's new boyfriend, while Serena keeps her past a secret from Aaron, but Dan spills the beans.

Season 3, Episode 11
The Treasure of Serena Madre
Serena faces an awkward Thanksgiving dinner with unexpected guests. Meanwhile, Blair suspects her mother of keeping a secret, and Jenny seeks revenge against Eric.

Season 6, Episode 8
It's Really Complicated
Serena and Dan's first Thanksgiving together is filled with drama as everyone has their own agenda.
St. Valentine's Day episodes:

Season 5, Episode 15
Crazy, Cupid, Love
Blair plays matchmaker on Valentine's Day while Georgina crashes Nate's party, and Serena witnesses something shocking.