Friends mastered the art of the flashback with numerous trips into the past, but the most memorable trip down memory lane involved Chandler's Flock of Seagulls haircut, Monica's fat suit and a poorly placed steak knife. Oh, and did we mention Rachel, pre-nose job? They may have looked different, but they were still our quirky, lovable Friends.

In the first flashback episode of the series, we meet Homer and Marge as seniors in high school in 1974. Not only did we love seeing their youthful hairstyles (Marge's was much less bouffant; Homer had hair!), but it was sweet to know that they were destined to be together from the start — despite a rather determined Artie Ziff (Jon Lovitz) trying to pull a fast one. Bonus: Music from the Steve Miller Band and The Carpenters.

Mad Men has used many well-timed flashbacks, but this one, which shows how Don Draper launched his career at Sterling Cooper, takes the cake. After salesman Don sells Roger Sterling a fur for his mistress (Joan!), Don pitches a few ad ideas in hopes of winning a job. Roger balks, so Don shows up at the office and takes Roger out for a multiple-martini lunch. When Don shows up for work the next day, Roger is confused, but Don insists that Roger offered him the job. Was Don lying? We may never know, since Roger was sauced. Talk about a self-made man!

Before Will knew he was gay and Grace knew how to tame her frizz, these inseparable best friends were boyfriend and girlfriend back in college. Unfortunately for Grace, it only took one comment from a young (but surprisingly wise) Jack to convince Will he batted for the other team and to keep him from jumping into bed with a very horny Grace. All things considered, its amazing she didn't have more issues with the opposite sex after a rejection like that.

Fringe delved into the past to dissect how Olivia's powers first manifested — and how the evil Walternate located his son. Our only question: Why don't Peter and Olivia remember this? And after the Season 3 finale, did this really even happen? Trust the Fringe flashbacks to make us even more confused than we were before.

How do you pick the best flashback from a show built on flashbacks (not to mention flash-forwards)? It took us a while, but we're going with this episode, in which each member of the quintet reminisces about their most memorable times with Marshall's old car. It's here we first see the pretentiousness of College Ted ("My parents live in Ohio; I live in the moment.") when he recounts "Fieroasco" and/or "100K Fiasco": College Marshall offers to drive him home for Christmas during their freshman year, and they end up cuddling together and bonding during a snowstorm — planting the seeds of a legendary friendship. Too bad Fiero never made it to 200,000 miles.

This is the first time that Dexter Morgan — blood spatter expert by day, vigilante serial killer by night — relives the long-suppressed childhood memory of himself at 3 years old, crying and sitting in a pool of blood. Not only is this the first time we've seen adult Dexter truly disturbed, but it gives us insight into the traumatic past that shaped his twisted psyche. Flashbacks are important in Dexter, and this is where it all began.

Everybody Loves Raymond — "The Wedding, Part I and II" Season 2 ended with a two-parter that focuses on a simple question: Why did Debra marry Ray? The flashbacks to their wedding featured many fits of nervousness for Ray, which Frank tried to combat with whiskey. The results are hilarious, but despite Ray giving Debra "one more chance to say no," she choses Ray.

Over a bottle of wine (or two), Neal shares with Peter exactly how he went from small-time bond forger to major criminal mastermind in the span of only a few years and more about the woman that got in the way: a rare appearance from the late Kate. Although instructional, the best part of the episode was the hair — specifically Peter's Magnum-esque mustache and Mozzie's hilarious toupee and goatee.

Fans finally got to meet the oft-mentioned but never-seen Katherine Pierce (hey, she sort of looks like Elena!) in this trip back to 1864. Many moons before Katherine's appearance in present-day Mystic Falls, this early Season 1 episode laid the groundwork for Stefan and Damon's longstanding and complicated rivalry, and so much more.

Before Bailey was the Nazi of Seattle Grace, she was a sweet and soft-spoken intern (with a very spirited hairdo) who began to outshine her resident. The episode also featured a flashback to the beginnings of the Chief and Ellis Grey's relationship, as well as when Alex faked that he was the "elevator guy" to get Callie into bed.

In "Fool for Love," we get to see the beginning of Spike, formerly a meek poet named William in 1880 London. But after he's turned by Drusilla, he becomes a killing machine, obsessed with seeking out slayers. He vanquish a Chinese slayer in 1900 — but not before she scarred — and another in an NYC subway. In the middle of Season 5, and Spike's growing infatuation and tenderness toward Buffy, it nice to see him as his formal self — in full rampage mode.

How was 30 Rock going to re-create its signature quickie flashbacks on its live episode? With a little help from some Saturday Night Live friends — namely Julia Louis-Dreyfus, who cheekily played "Flashback Liz" in one meta cameo. "Why are you better-looking in your memory?" Jack asks. "My memory has Seinfeld money," Liz replies.

Ah Christmas, 'tis the season for gingerbread, Santa Claus and … finding out that your dad fights monsters for living? This Season 3 episode traveled back to 1991 to show the first time Sam found out what their dad really did for a living. Dean tries to protect his younger brother and tells him the monsters won't get John Winchester, but Sam falls asleep crying. Also, this is the same Christmas that Dean received his gold amulet.

The only thing more heartbreaking than watching Tobias Hankel (James Van Der Beek) torture and drug poor Reid is revisiting the super-genius' troubled childhood, during which his dad left him and his schizophrenic mother, Diana (Jane Lynch), to fend for themselves. That all led to 18-year-old Reid (Matthew Gray Gubler with a hair part in the middle!) committing Diana to a sanitarium. But why did Daddy Reid really leave the fam? (Spoiler alert!) In another flashback in Season 4, he reveals that he couldn't deal with harboring the knowledge that Diana had witnessed a murder. Father of the year!

How to pick the greatest flashback from this show, which jumped through time in almost every episode? Look no further than "Walkabout," the first John Locke flashback. The episode concerns itself with Locke planning an spiritual hunting journey in the Austrailian Outback, only to be rejected because he's in a wheelchair. Of course, back in present day, Locke is able to walk and hunt without any assistance. The pilot might have featured scary smoke monsters, but this episode was when we really began to learn just how magical the Island was.