American Gladiators (8-10 p.m., NBC10) - The two-hour second-season premiere, in which ordinary people are pitted against the show's "gladiators" - action stars and stunt artists - in strength and endurance contests.

Gossip Girl (8-9 p.m. CW57) After Georgina spills the beans on why Serena left town for boarding school, Serena reverts to her old ways, causing Blair, Nate and Chuck to set down their own baggage and try to help.

American Experience (9-11 p.m. WHYY TV12) - Franklin Delano Roosevelt is profiled.

House (9-10 p.m., Fox29) - In the opener of this two-part season ender, House loses a big chunk of his memory due to a bus accident. He has a lingering feeling that someone else on the bus was deathly ill, but he can't remember the details.

Late Show With David Letterman (11:35 p.m.-12:35 a.m., CBS3) - Stupid Pet Tricks; actor Shia LaBeouf; N.E.R.D. performs.

The Tonight Show With Jay Leno (11:35 p.m.-12:35 a.m., NBC10) - Actor Jack Black; musician Clay Aiken.

Jimmy Kimmel Live (12:05-1:05 a.m., 6ABC) - Actor Robert Downey Jr.; Mario, the eighth celebrity eliminated from Dancing With the Stars; Lyfe Jennings performs.

The Late Late Show With Craig Ferguson (12:35-1:35 a.m., CBS3) - Actor John Stamos; author Judith Smith-Levin; Jaymay performs.

Late Night With Conan O'Brien (12:35-1:35 a.m., NBC10) - Actor William Shatner; wine connoisseur Gary Vaynerchuk.