TONIGHT'S MUST-SEE

"A Charlie Brown Christmas," 7 p.m., ABC. After 40 years, this cartoon remains one of TV's greatest achievements. That started by breaking all the usual habits. It used real kids as voice actors and a sparse, jazz score. It also quoted scripture. Most important, it did everything well. Funny, sweet and moving, this is a classic.

"Billboard Music Awards," 7 p.m., Fox. The awards simply mark sales success, not quality. Still, this show assembles lots of talent. Performing tonight are R. Kelly, Green Day, Toby Keith, Carrie Underwood and Ciara. One special honor (Artist Achievement Award) goes to Kanye West. Another (Century Award) goes to Tom Petty.

OF NOTE

"Knights of the South Bronx," 6, 8, 10, midnight, A&E. In real life, a chess team from a poor area became national champs. That fascinating story is told with lots of fictional touches. There's great work from director Allen Hughes and star Ted Danson.

"The Triangle," 7, 9, 11 p.m., Sci Fi Channel. In the opener of this three-night mini-series (rerunning at 5 p.m.), a team of skeptics found perplexing events in the Bermuda Triangle. Tonight, they try to return to normal lives but find they can't.

"Middle Sexes: Redefining He and She," 7:30 p.m., HBO. This documentary examines our attitudes toward transsexuals and informs us that more than 1 percent of all babies born may not fit neatly into male or female categories.

"Chasing Christmas," 8 p.m., ABC Family. If you missed Sunday's debut of this comedy, catch it now. It's a clever "Christmas Carol" take-off starring Tom Arnold.

"Commander in Chief," 8 p.m., ABC. For people who were slow to discover this hit show, here's a third chance to see the pilot. Geena Davis is solid as the vice president thrust into the presidency.