NBA playoffs (6 p.m., TNT): Celtics at Cavaliers

Big Bang Theory (7 p.m., Ch. 2): Penny throws Leonard a surprise party.

Dancing With the Stars (7 p.m., Ch. 4): The final four couples perform.

American Gladiators (7 p.m., Ch. 5): A new season of this dreadful show — which appears to have been thrown together on a budget of about $1.98 — begins.

Bones (7 p.m., Ch. 13): An aspiring singer is murdered.

Gossip Girl (7 p.m., Ch. 30): Georgina divulges the real reason Serena fled from Manhattan.

How I Met Your Mother (7:30 p.m., Ch. 2): Britney Spears returns as Abby — and both Abby and Barney want to get back at Ted.

Two and a Half Men (8 p.m., Ch. 2): Charlie is attracted to an older woman.

House (8 p.m., Ch. 13): House loses part of his memory in an accident — and when it starts to come back, he remembers what could be a desperate medical situation.

One Tree Hill (8 p.m., Ch. 30): Lucas and Brooke both get bad news.

Samantha Who? (8:32 p.m., Ch. 4): Sam puts her relationship with Todd on hold. (Season finale)

CSI: Miami (9 p.m., Ch. 2): Apparently Tom Sizemore is out of prison, because he's guest starring as a shady private detective.

The Bachelor: London (9 p.m., Ch. 4): Matt chooses in the season finale of this unreal reality show.

Medium (9 p.m., Ch. 5): Joe discovers the truth behind Meghan's plans for his invention. (Season finale)