Flashbacks are boring. Often, they use stock footage and make it seem like the story's on hold. A not-so-recent subversion of the typical flashback is to have the flashbackee be an observer.
He might walk around and watch his younger self, "Was I really like that?" Perhaps another person is in there with him, berating him for a pathetic life choice or showing him what he has to live for.
Makes for an interesting sequence.
Similar to the Exposition Beam, which essentially transfers these memories from one character to another, allowing them to experience their own POV. Related to Time Travel, particularly Intangible Time Travel.
In Dr. Kishiwada's Scientific Affection Dr. Kishiwada uses virtual reality security cameras to go back into the past, find the culprit of a crime and trace him back to his "hideout". Being Dr. Kishiwada this is all pretty normal stuff.
In Tsubasa Reservoir Chronicle, Syaoran picks up a magic book that shows him Kurogane's past. He is unable to close the book until he finishes watching Kurogane's youth, though he can't interfere.
Most of Millennium Actress is a variation of this. As the eponymous character tells her life story to a documentarian and his cameraman, the events are shown, with the two men as observers—and later, participants.
Hilariously lampshaded when it cuts back to the present day interview— and they're acting the flashback out.
Haruka does this all the time. Also, future badasses Karasu and Fukurou. ..sort of. And Yuu's mother, Miyuki Gotou, also did it once.
In Mirai Nikki, Yukki is shown Yuno killing Yuno in this way. It turns out this Yuno is from an alternative timeline who came back to take over and be with Yukki once more.
20th Century Boys: The Bonus Stage in Friend Land is effectively a Pensieve Flashback to the area and time period Kenji and his classmates grew up in, albeit one where you can interact with the virtual people and certain details are missing. This is played with in at least one scene where what appeared to be a genuine flashback only the audience sees is really just another visit to Bonus Stage.
Noah puts the Kaiba brothers through these during the Virtual Nightmare arc of Yu-Gi-Oh!.
Spectacular Spider-Man Annual #14 has Spidey find a computer disk that allows him to explore the events of Norman Osborn's life.
In one version of Hal Jordan's origin story, his ring does this so he can experience the final battle of his predecessor, Abin Sur.
Also, the use of No Fourth Wall sometimes let other characters speak to the audience, such as when he asks his former classmates from elementary school what they're doing now.
Little girl: I'm into leather.
The film Eternal Sunshine of the Spotless Mind halfway uses this, in that the character who is flashing back (as his memory is being erased) is participating in the action, but he's also commenting on it to his girlfriend. When he breaks course and flashes back to his childhood, he and his girlfriend are still themselves (that is, played by Jim Carrey and Kate Winslet), but they are still acting out his memories (he's in his five-year-old's rocket pajamas, she's dressed up like his mom. It plays out a lot better on-screen.
The Made-for-TV Movie based on the book The Five People You Meet in Heaven by Mitch Albom is chock-full of this. In it, an elderly man named Eddie dies in a roller coaster accident at Ruby Pier, the fairground where he worked his entire life. When he goes to heaven, he meets five people who tell him the meaning of his life and tell things from their lives as well. The person who did it the most was Ruby, the namesake for Ruby Pier.
Ghosts in Pact serve this purpose. Being essentially an imprint left on the world by an event of great emotion, trauma, or inspiration, they replay that moment to whoever interacts with them. Notably, though death is the most common source of ghosts seen in the story, the event that creates a ghost doesn't have to kill the person that it involved. At one point, Conquest weaponizes this feature to summon the ghosts of the most traumatic experiences Blake Thorburn has ever had and forces him to relive them.
Live Action TV
In Angel, Faith and Angelus enter Angel's subconscious thanks to a mystical drug that links their minds. They observe Angel's past mistakes, snipe at each other and eventually start fighting... inside the flashback.
In an episode from the 2000s Battlestar Galactica, "Maelstrom", a figure who looks like her enemy Leoben guides Kara "Starbuck" Thrace through flashbacks of her troubled relationship with her mother, in order to help her achieve closure and embrace her destiny.
The Frasier episode "Daphne Returns" had a couple of flashbacks of past Niles and Daphne moments, with present day Frasier and Niles observing.
The best one is a memorable scene from older episode that Frasier finds so preposterous (largely due to a lack of context) that he denies it could have possibly happened.
The appropriately named Star Trek: Voyager episode "Flashback" has a telepathy-induced flashback. Unique in that one of the characters observing the events wasn't there when they actually happened (In fact, she wasn't even born yet). It gets even weirder when the flashback somehow malfunctions (!?) and the characters in the flashback can suddenly see and react to the observers.
The person whose memories they were had to act his role in them all along. The remembered people just stopped ignoring his asides and his "guest."
And it was subverted when the exact memory that was troubling the flashbackee isn't even his own, but planted there by a virus.
Also, TNG often used the holodeck to recreate events or memories as an investigative aid. Troi has all the victims of subspace alien abduction in "Schisms" relate their experiences and recreate the scenario on the holodeck.
In the sitcom King of Queens, One episode has each of the three core characters going to a therapist. Each time the character and the therapist become observers of some kind of event in that character's childlife. They then go on to argue with someone in the flashback. The last one even has him getting into a fight with his younger self.
There was a short-lived ABC TGIF sitcom where two brothers had a Flash Back to their childhood. It starts out played straight, but then the adult brothers enter the scene to argue "that's not how it happened" or some such. At the very end, the adults leave, but on the way out one decides to screw with the kids' heads by telling them "Darth Vader? Luke's father."
The sensory deprivation tank in Fringe coupled with LSD and electrodes allowed Olivia to experience John Scott's memories as an observer in this manner.
As with all flashback tropes, this was used on LOST. The episode "Maternity Leave" features Claire recovering a memory of her abduction by "watching" herself talking with Ethan outside the Staff Station.
Mad Men has something like this in the first episode of season three, where Don looks on as flashbacks show how he was conceived, born and adopted. However, they're obviously not his own memories, since he was a prostitute's worst fear/a fetus/a newborn when they took place.
House gets these in "Baggage" and, technically, in "Three Stories"
The Dead Zone: In the TV series, some of Johnny Smith's visions work in this manner and he can even rewind or replay the vision in Bullet Time to get a better perspective of the events he's seeing.
Pops up a few times in Charmed, firstly in "A Paige From The Past" where Paige is sent back in time to her teenage years to relive her parents' last day. She becomes herself but Leo sits on the sidelines to guide her. A similar version happens later on when Paige takes Kyle Brody back to his childhood but he doesn't assume his younger self.
Leo's vision quest in "Someone To Witch Over You" where he is shown flashbacks of his life with Chris as his guide.
Phoebe takes another one in the episode "Generation Hex" where she sees all her past loves.
MythQuest: Alex travels into a Norse myth and encounters Thor. He has questions about the history between Thor and Loki, so Thor brings him into two different flashblacks that they observe together.
The Vampire Diaries' Season 4 premiere has Elena experience a buried memory as though she's seeing it from outside her body.
The premiere of Agents of S.H.I.E.L.D. feature the team using videotape footage and a holographic computer simulation to recreate a laboratory explosion.
A rather interesting case occurs in Final Fantasy VII as a crucial part of game's story. The heroine Tifa enters the catatonic hero Cloud's mind and helps him sort through his muddled memories. Together, she and Cloud (his subconsciousness, really) go over experiences they shared in the past to determine what memories were real, which were invented, and which were implanted.
The pyreflies can form visions of people or events when there are enough of them, such as in the Farplane or especially Zanarkand Dome, where you see visions of Jecht, Auron, and Braska.
When you reach Zanarkand and find out that Zanarkand is the Fayth's dreams of their memories of the old city, making it one big Pensieve Flashback that carried on where the real city left off when it was destroyed.
The Memory Maze in Wild ARMs 2, which had the Sword Magess, Anastasia guiding Ashley through her memories.
In the third act of Our Town, Emily, now deceased, is given the chance to relive one day of her life. She is advised to make it an unimportant one, since the experience of watching herself alive will be painful for her. The date she chooses is that of her twelfth birthday (Tuesday, February 11th, 1899).
The nameless protagonist of HERO, when he picks up a compass containing a memory, experiences one of these—though he experiences it in first person, the only thing he can do that deviates from the memory is to think, and technically, it's Eira's memory.
In Juathuur, Arvval and Faevv watch this way Faerun's disappereance.
In Blip, Liz's portion of the "Rashomon"-Style flashback involves Hester and Mary stepping directly into her memory. ("This is cool, right? Just like inHarry Potter.") Memory!Liz within the flashback acts as the mouthpiece for modern-day Liz, and Hester (briefly forgetting that these are not actual events) punches one of the memories.
The dream bubbles in Homestuck. They act both as the dream world and the afterlife, and are composed of the memories of the dreaming/dead people. The main twist is, originally when dreaming the character's memory is retold verbatim, but once they realize it isn't a memory they are free to manipulate stuff at their will.
Psychics in We Are All Pokémon Trainers can use their powers to allow people and Pokémon within a certain radius to see the memories of themselves and others as observers. Aura can be kneaded into the projection to get around the difficulties most Dark types have with this.
Teenage Mutant Ninja Turtles did this in the 2003 series: the Utroms show the Turtles and Splinter why and how they landed on Earth via virtual simulation pods. Then Stockman hacks into the system and past-Shredder stops ignoring the Turtles...
An episode of Chowder has this be the solution to Mung's teacher telling everyone awful stories about him. They make him tell the story, then jump into his flashback to alter the past. It works flawlessly...except that Chowder decided to grab his past self and pull him to the present...
Avatar: The Last Airbender does this sometimes. When Aang and Roku visit Roku's past to teach Aang in 'The Avatar and the Fire Lord', Roku is able to see his past self.
In the season 4 premiere "Princess Twilight Sparkle", Twilight drinks a potion provided by Zecora that allows her to peer into Equestria's past. She sees Celestia's battle with Nightmare Moon, then Celestia and Luna's original confrontation with Discord, then finally Celestia and Luna finding the original Elements of Harmony at the Tree of Harmony.