TONIGHT'S MUST-SEES

"Boston Legal," 9 p.m., ABC. At its worst, "Legal" can be broad and silly. At its best, including tonight, it takes your breath away with its brilliance. One section has the rich people of Nantucket wanting their own atom bomb. Yes, there's a method to the madness. Another is a right-to-die debate involving Shirley's father, who has descended deeply into Alzheimer's disease. There are quietly stunning moments, as Alan (James Spader) reflects on Denny Crane, the colleague in early stages of Alzheimer's.

"The Biggest Loser" finale, 7 p.m., NBC. This starts by telling which person has been ousted by viewers. That leaves three people going for the $250,000 prize. Also, previous contestants return for a weigh-in.

OF NOTE

"American Idol," 7 p.m., Fox. The final seven contestants perform.

"Frontline: Sick Around the World," 9 p.m., PBS. T.R. Reid, a foreign correspondent for the Washington Post, says he's seen national health plans that work. Here, he visits England, Germany, Japan, Taiwan and Switzerland. The catch: The systems indirectly limit the incomes of doctors and drug companies.

"Independent Lens: King Corn," 10 p.m., PBS. Two city guys go back to their granddads' home town (Greene, Iowa) to raise an acre of corn. It's a slow hour, but tells a lot about modern life in big-time farm country.

"48 Hours Mystery," 9 p.m., CBS. This is a replacement for "Secret Talents of the Stars," which has already been pulled. It looks like those talents were meant to remain secret.

"The Riches," 7 p.m., FX. In a fairly good episode, one son is on the run and another needs a way to save his dad.

"Work Out" season-opener, 8 p.m., Bravo. Jackie Warner, who dumped her previous girlfriend last year, is gaga over Brianna, a young bartender. They kiss profusely — even during a dinner party — stirring grumbles from everyone else. Stirring more commotion is Gregg Plitt, a new trainer with an impossibly molded torso.