If you only watch television one night this year, you’d better tune in this evening. It’s easily the most exciting and over-programmed night of the year. Tonight marks the conclusion of TV’s most nail-biting drama; the last night of competition on the most hyped and successful “reality” talent show; the very last episode of a TV classic; the conclusion of an intelligent, if flawed, TV miniseries; and the season finales of about a dozen other shows. You couldn’t watch it all if you tried. And believe me, I’ve tried.

• There’s no way on earth Jack Bauer can wrap up all of the loose ends on tonight’s “24” (8 p.m., Fox). For starters, his heart has stopped beating on a regular basis, his latest “ally,” the treacherous Sherry Palmer, is suffering from a knife wound, and together they have just driven off the highway. His confederates at CTU are under arrest and his pal the president has been deposed. Years from now, serious thinkers and pop historians trying to gauge the temperature of our current political-military-cultural climate will be writing about this season of “24.” It ends tonight. Don’t dare miss it.
• Buffy is dead. And this time it’s for keeps. OK, the Slayer can never die, but the much-praised and ratings-challenged “Buffy the Vampire Slayer” (7 p.m., UPN) airs its last episode tonight. It’s about two years overdue. For all of the current hype, “Buffy” peaked a long time ago. With the exception of the brilliant “musical” episode two seasons back, this show has run out of new tricks. I won’t give away too many secrets about the wrap-up, but look for a witty and well-done scene between Buffy and Angel. Is this goodbye, or merely a setup for her cameos on his still surviving WB series? I’ll never tell.
• Rory Gilmore, Lorelai’s pretty, perfect, know-it-all daughter, graduates tonight from her posh prep school on the third-season finale of “The Gilmore Girls” (7 p.m., WB). And wouldn’t you know, she’s the valedictorian. While Buffy and her Scooby gang are battling the forces of hell at Sunnydale High, Rory’s biggest problem is asking her rich grandparents (the perfectly cast Edward Herrmann and Kelly Bishop) for the dough to put her through Yale. Life is tough.

We should all hate Rory. Jack on “Will & Grace” made a crack about her on a recent episode. But as much as we could resent Rory’s wonderful life and perfect cheekbones, we don’t. Why? Because she’s that rare television creation — a teenager who is also a good kid. She’s not an airhead, or a brat, or merely a babe — she’s the kind of person who makes grown-ups proud. We all know, or knew, a few of those kids.

That’s why millions of viewers won’t be embarrassed to get a bit misty tonight when she delivers her graduation speech. Seriously, if you like this show, have a hanky handy — you’ll need it.

Tonight’s other highlights

• “American Idol” (7 p.m., Fox) comes down to the last battle of the ballads between Alabama’s super-sized Ruben and Clay, the pixie tenor from the Tar Heel State.
• The two-part miniseries “Hitler: The Rise of Evil” (8 p.m., CBS) concludes.
• Why is the UPN the last-place network? Because they’re foolish enough to launch a brand-new series, “America’s Next Top Model” (8 p.m., UPN), on a night when everybody is watching series finales.
• Red tape dooms Andy and Connie’s marriage plans on the 10th-season finale of “NYPD Blue” (9 p.m., ABC).

Late night

Jim Carrey and Chevelle appear on “Late Show with David Letterman” (10:35 p.m., CBS) … Jay Leno welcomes Albert Brooks and music from The Thorns on “The Tonight Show” (10:35 p.m., NBC).