TONIGHT'S MUST-SEE

"30 Rock" season opener, 7:30 p.m., NBC. Fresh from its Emmy as best comedy series, "30 Rock" has its funniest episode so far. Liz (Tina Fey) is back from the hiatus and thinks she's happy. People convince her she shouldn't be without a guy. Meanwhile, Jack (Alec Baldwin) has a scheme to digitally insert Jerry Seinfeld into every show. It's a fine idea — until the real Seinfeld confronts him. One side story (Jenna gained weight in a "Mystic Pizza" musical) is funny. Another (Tracy squabbles with Kenneth) is merely overdone. The real strength is in the main story. Seinfeld glides through it even mocking the network. For a half-hour, NBC is back to its Thursday best.

"Grey's Anatomy," 8 p.m., ABC. Hopes have definitely been dashed. Burke's mom (Diahann Carroll) returns to gather his things; Cristina returns the wedding presents. Meanwhile, Meredith is reluctant to chat with her sister who now a surgery resident.

OF NOTE

"Last One Standing" debut, 6 p.m., Discovery Channel. This series starts with six champion athletes whose skills range from kickboxing to croquet, from dirt-biking to salsa dancing. Then they are plunked into unfamiliar areas competing in tribal games. The opener has them wrestling with the Kalapalo people of Brazil.

"Ugly Betty," 7 p.m., ABC. Betty gets a tempting offer from the scheming Wilhelmina, but she worries about her loyalty to Daniel. Also, Henry is back.

"My Name is Earl," 7 p.m., NBC. Earl is still behind bars and his brother, Randy, is still trying to join him there. Now comes a break: Earl might get a lighter sentence if he can broker peace among the prison gangs.

"The Office," 8 p.m., NBC. Ryan is back from company headquarters, forcing his old colleagues into the digital age.

"CSI: Crime Scene Investigation," 8 p.m., CBS. Here's something new to worry about: A murder is committed in an extremely dark restaurant.

"Without a Trace," 9 p.m., CBS. A man and his daughter are missing. The team wonders if that's related to his job cleaning up crime scenes.

"ER," 9 p.m., NBC. Neela fidgets because she's eager to be released as a patient. Meanwhile, her colleagues are struggling with the demands of Dr. Morretti (Stanley Tucci), their new boss. Also, a simple stomachache becomes a bigger problem.