TONIGHT'S MUST-SEE

"So You Think You Can Dance," 8 p.m., Fox. Tonight, two more dancers are dropped. That trims the once-huge field to six.

"It's Always Sunny in Philadelphia," 7 p.m., FX; repeats at 8, with another episode rerunning at 7:30 and 8:30. This oddly entertaining show often gets by on sheer perversity. Each character is shallow and self-centered; tonight, that hits an extreme. A water stain at the bar looks a tad like the Virgin Mary. Soon, Dee is trying to seduce a young priest into blessing the stain; her dad (Danny DeVito) is trying to prop up an old priest to do the same. Mac and Charlie are turning themselves into evangelists.

OF NOTE

"Master of Champions," 7 p.m., ABC. Here's the season finale for this show, which is filled with people who have odd skills.

"Big Brother: All-Stars," 7 p.m., CBS. It's time for another person to be ousted from the house.

"Grey's Anatomy," 8 p.m., ABC. While Izzie plans a party, everyone has bigger problems at the hospital. That includes a heart operation, one patient who is an ex-smoker and another who is addicted to pain-killers.

"CSI: Crime Scene Investigation," 8 p.m., CBS. Grissom and Catherine try to figure out if three deaths are related.