Downton Abbey (3pm, UNC-TV) - If you've heard about it but haven't seen it, now's your chance to catch up. There's a marathon of Season 1 starting today at 3, with all four parts running back-to-back. A Season 2 marathon takes place next Sunday.
The Christmas Heart (8pm, Hallmark) - Neighbors in a close-knit community realize their Christmas tradition of lighting luminaries cold help a teen receive a heart transplant.
The Walking Dead (9pm, AMC) - Tonight's mid-season finale, a situation at Woodbury throws inhabitants for a loop and forces Andrea to take charge, while a new threat arises at the prison. Expect some shocks and a nice little cliff-hanger. Season resumes in mid-February.
Boardwalk Empire (9pm, HBO) - In the Season 3 finale, Nucky sacrifices a key asset to Rothstein in an effort to disrupt the Rosetti-Masseria alliance and take control of Atlantic City once again. Meanwhile, Chalky and Capone are unlikely allies in the war against Masseria. That Gyp Rosetti (Bobby Cannavale, right) is one crazy bastard. I almost hope he survives for Season 4.
CNN Heroes: An All-Star Tribute (9pm, CNN) - Anderson Cooper hosts the sixth annual salute to everyday people for their work improving the world. Celebrity presenters and performers appear.
Finding Mrs. Claus (9pm, Lifetime) - Santa's neglected wife goes to Las Vegas to help a girl with a Christmas wish. When Santa finds out, he travels to Vegas to make amends and ends up putting Christmas at risk.
Revenge (9pm, ABC) - Nolan must face an element from his past, while Daniel's position at his family's company is questioned.
Oprah's Next Chapter (9pm, OWN) - Oprah talks to Mr. and Mrs. Abraham Lincoln (also known as Daniel Day-Lewis and Sally Field).
The Good Wife (9:30pm, CBS) - Will defends a man accused of murder, and Alicia attempts to influence the outcome of the case by assisting a prosecutor in a nearby county who is trying another man for the same crime.
Homeland (10pm, Showtime) - Brody and Walden develop a chink in their political relationship, and it may impact their future. Elsewhere, Dana and Finn come to an understanding, and Carrie discovers she is not as looped in as she thought.