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Friends, ''The One Hundredth''
A.K.A. ''The One Where Phoebe Gives Birth to her Brother's Triplets,'' finishing off one of the sitcom's most memorable arcs — and giving Lisa Kudrow a chance to really show off her range as an actress. (Kudrow, who had just won a supporting statuette at the Emmys, submitted this episode for the next year's awards; though she got a nomination, she ultimately lost to Kristen Johnston of 3rd Rock from the Sun.) Sure, there's also some important Monica (Courteney Cox) and Chandler (Matthew Perry) business and a truly great Joey subplot (''kidney stooones)...but what we'll always remember from this half hour is a teary, exhausted Phoebe holding those babies close, knowing that her time with them has finally come to an end. —Hillary Busis
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Buffy the Vampire Slayer, ''The Gift''
Talk about a leap of faith! Buffy's season 5 finale saw the series exit from The WB to UPN (the two networks ultimately merged to form The CW), as the Slayer (Sarah Michelle Gellar) flung herself into a portal to another dimension to defeat Big Bad Glory (Clare Kramer) and save sister Dawn (Michelle Trachtenberg). As Buffy's own tombstone read, ''She saved the world a lot.'' And she wasn't done yet. Thanks to creator Joss Whedon's fearless storytelling, Buffy emerged from the abyss to rack up another 44 episodes?though none of them ever quite reached the heights of ''The Gift.'' —Lanford Beard
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NCIS, ''Life Before His Eyes''
The series' flashback- and alternate universe-filled 200th episode was far from your average NCIS episode, but a treat for diehard fans. Per the storyline, near-death Gibbs (Mark Harmon) was given a guided tour of important moments in his life by Mike Franks (Muse Watson), and it featured appearances from several people from the past including Kate (Sasha Alexander) and Director Jenny Shepard (Lauren Holly). The result was a deeper understanding of how Leroy Jethro Gibbs came to be, and the episode reinforced the idea that his team — and NCIS, in a way — would not be the same without him. —Sandra Gonzalez
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The Big Bang Theory, ''The Recombination Hypothesis''
Say what you will about Chuck Lorre's ratings juggernaut, Bang know how to spin a good title. The 100th episode stayed true to its name, hypothesizing (via dream sequence) what would happen if their original will-they-or-won't-they couple, Leonard (Johnny Galecki) and Penny (Kaley Cuoco), ''recombined'' after breaking up two seasons before. Unfortunately, the scientific method in this ep stopped at step three, leaving us without a conclusion on the off-again couple's relationship status. —Jodi Walker
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Grey's Anatomy, ''What a Difference a Day Makes''
In the show's 100th episode, Izzie (Katherine Heigl) is busy preparing for the wedding of Meredith (Ellen Pompeo) and Derek (Patrick Dempsey) when her hallucinations of Denny (Jeffrey Dean Morgan) return, which means she has another brain tumor. Elsewhere, Meredith performs her first ever solo surgery and George (T.R. Knight) struggles when he fails to save a group of college graduates who come into the ER after a bad car accident. But when Meredith gets out of surgery, Bailey (Chandra Wilson) and Derek inform her of their plan. And in a surprise moment, Meredith hands her wedding gown to Izzie, who ends up saying ''I do'' to Alex (Justin Chambers) as we all cry — George walked her down the aisle! The episode ends with Alex shaving his new wife's head as she tells Denny's ghost to leave her alone with her new husband. —Samantha Highfill
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Law & Order: SVU, ''Authority''
Robin Williams guested — and snagged an Emmy nod — as Merritt Rook, a sadistic, anti-authority prankster who poses as an NYPD cop and tricks a fast-food employee into submitting herself to a humiliating strip search. Spun out from a series of real-life incidents, SVU took an already chilling story and cranked up the volume to 11, adding layers of twisted motivation for Rook's action and forcing Stabler (Christopher Meloni) to listen to the blood-curdling screams of his partner Benson (Mariska Hargitay). And all that's without mentioning a literally explosive grand exit for Rook and Williams. —Lanford Beard
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The Simpsons, ''The Simpsons 138th Episode Spectacular''
The animated giant's 100th episode (''Sweet Seymour Skinner's Baadasssss Song'') came and went without any fanfare in season 5. Two years later, though, The Simpsons decided to celebrate a random milestone with this brilliant clip show, hosted by the late, great Troy McClure (Phil Hartman). The resulting spectacular managed to be both a parody of gratuitous network TV filler and a trivia-packed treat for fans — even if some of that trivia turned out to be patently false. (Psst: When the cashier rings up Maggie at the grocery store in the opening sequence, the register doesn't really say ''NRA4EVER.'') —Hillary Busis
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Supernatural, ''Point of No Return''
In the 100th episode of the Winchester brothers ''hunting demons and saving people,'' Dean (Jensen Ackles) packed up his things and prepared to hand over his meat suit to Archangel Michael. But when he and Sam (Jared Padalecki) were reunited with their brother Adam (Jake Abel), things got a little complicated. Let's just say that emotions ran high. Castiel (Mischa Collins) hit his breaking point with Dean (and took it out on Dean's beautiful face), Sam put his faith in his big brother, and Zachariah (Kurt Fuller) said his final farewell. At the end of the hour, Dean managed to escape his destiny yet again, but things didn't look great for baby brother Adam. —Samantha Highfill
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Bones, ''The Parts in the Sum of the Whole''
The fact that Bones (Emily Deschanel) and Booth (David Boreanaz) are now married helps make the show's 100th episode, in which the pair had a hugely emotional exchange about their push-and-pull status, a little less depressing. But at the time, it was hard to find a dry eye among fans when Booth laid it out for Brennan. ''When you talk to older couples who have been in love for 30 or 40 or 50 years,'' he told her, ''it's always the guy who says, 'I knew.' I knew. Right from the beginning.'' It only took 72 more episodes for them to make it official. —Sandra Gonzalez
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How I Met Your Mother, ''Girls vs. Suits''
In the show's 100th episode, Barney must decide whether to give up suits in order to bag MacLaren's hot bartender, played by Stacy Keibler. He chooses his suits over his suitor. The episode ends with a pull-out-the-stops musical number — an homage to Gene Kelly's ''Singin' in the Rain'' (minus the precipitation). —Henry Goldblatt
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ER, ''When Night Meets Day''
The medical drama's 200th episode alternated between telling the stories of Carter's (Noah Wyle) day shift and what was supposed to be Pratt's (Mekhi Phifer) last night shift. By the end of the hour, Pratt had decided to stick around, Romano (Paul McCrane) had decided to have his arm amputated, and Carter had decided to go to Africa after receiving an emergency phone call from Kovac (Goran Visnjic). —Samantha Highfill
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The Office, ''Company Picnic''
The 100th episode of The Office was also the fifth-season finale, and it brought the laughs — Michael (Steve Carell) and Holly's (Amy Ryan) ''SlumDunder Mifflinaire'' skit — as well as heartwarming moments, such as when an injured Pam (Jenna Fischer) discovers she pregnant. She and Jim's (John Krasinski) silent joy (as well as Jim's ''Send in the subs!'' to the camera) highlighted in the closing seconds what fans have always known: This show wasn't just funny, it could also be, despite Michael's best efforts, really touching. —Erin Strecker
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Gossip Girl, ''G.G.''
XOXO, Georgina? The posh CW drama's 100th episode was one of its most shocking. Blair (Leighton Meester) walked down the aisle with her royal fiancé Louis (Hugo Becker) right after she and Chuck (Ed Westwick) admitted their love for each other, but then ditched her reception with her other love interest, Lonely Boy Dan (Penn Badgley). And that wasn't all, Upper East Siders: Georgina Sparks (Michelle Trachtenberg) also returned and was seemingly revealed to be Gossip Girl. OMG, indeed. —Shirley Li
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Late Night with Conan O'Brien, ''10th Anniversary Special''
Late Night with Conan O'Brien's quality varied from night to night, but the quirky comedian knew how to pull out all the stops for his hilarious 10th Anniversary Special. Those stops being, a barely clothed Will Ferrell, Triumph the Insult Comic Dog and this exchange between Conan and Mr. T —
Conan: But Mr. T, we've been on the air for 10 years!
Mr. T: I know that, fool! But you only been funny for seven!
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Castle, ''The Lives of Others''
After a skiing accident lands him in a wheelchair, Castle (Nathan Fillion) thinks he witnesses a murder in the apartment across from him (sound familiar, Hitchcock fans?), but the murder mystery is actually an elaborately executed present to celebrate his birthday — and the show's 100th episode. When partner/girlfriend Beckett (Stana Katic) guesstimates they've solved ''maybe a hundred'' murders together since meeting, Castle toasts, ''Here's to a hundred more.'' —Katie Atkinson
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The Cosby Show, ''And So We Commence''
At the end of its eight-year run, The Cosby Show's two-part farewell — which added up to its 200th and 201st eps, respectively — showed several characters facing milestones of their own, too. The Huxtables said their final goodbye for two episodes as Theo (Malcolm-Jamal Warner) graduated from college, Denise (Lisa Bonet) discovered she was pregnant, and our favorite twosome Cliff (Bill Cosby) and Clair (Phylicia Rashad) whisked off the stage — and into a cheering, tearful audience — with a dance. That's what you call going out with grace. —Andrew Asare