TONIGHT'S MUST-SEES

"American Idol" finale, 7 p.m., Fox. Tonight, one of the Davids will be named the champion. Will it be Archuleta, 17, the sweet-faced elf with the strong, passionate voice? Or Cook, 25, with rock-star power? First, expect lots of hype, plus guest stars and the return of everyone in the final 12.

"Boston Legal," 9 p.m., ABC. For a scary stretch, producers weren't sure this smart series would be back. David Kelley wrote what could have been a series finale. The people of Concord, Mass., want to secede from the Union. Alan takes their case; Denny opposes. Two old friends are at odds. Breaking from the usual pattern, the show settles into one story for most of the hour. And yes, "Boston Legal" will be back next season, after all.

OF NOTE

"Law & Order," 7 p.m., NBC. In the first rerun, a teen has been killed and a pimp is a suspect; in the second, a psychiatrist is dead, with suspects plentiful. Then comes a new episode, revealing an elite prostitute ring.

"Lost," 7 p.m., ABC. The two-hour season finale won't be until May 29, but here are reruns of two terrific episodes that set it up. In the first, Jack is seriously ill, requiring a drastic step. In the second, Locke meets a mysterious stranger; we also get a perplexing look at his childhood.

"Depression: Out of the Shadows," 9 p.m., PBS. A cloud descends on many people, this documentary says; some 8 percent have major depression. The reasons can wobble between genetics and life's setbacks. Doctors find a chemical solution for some, but that differs in every case. Beautifully done, with a rich assortment of people, this is a darkly involving film. In the final half-hour, Jane Pauley — whose depression didn't hit until she was 50, leads a fairly informative forum.

"CSI: NY," 9 p.m., CBS. While holding hostages, a bank robber demands that an investigator prove he didn't fire the fatal shot.