A variation happens in Code Geass. After finding out Zero's identity, Shirley Fenette is shown writing in her journal about everything that's happened lately, but ends up tearing it out and throwing it away. Later, after she's been mindwiped, she finds the page under her desk.
Subverted in Tenshi Na Konamaiki, where one character comes to a confrontation with the genie ready to secretly take notes. He discovers a vital secret about the genie during the meeting, but their group gets Laser-Guided Amnesia at the very end. Shortly afterward, he discovers and pulls out the Note to Self... which contains not the secret bur rather some other perverted fact he had witnessed at that time, which given his character got the higher priority.
In JoJo's Bizarre Adventure Part 3, the heroes are attacked by a Stand-using baby who can attack and kill them in their dreams, and even if they survive, they won't remember the attacks after they wake up, because people quickly forget their dreams. Kakyoin warns himself about this by carving the message "BABY STAND" into his arm.
Part 6 had Jolyne sewing notes on her own skin using her own stand when she was under the effects of Jailhouse Rock which makes her unable to take in more than four pieces of information.
In Re:LIVE the main character is framed for murder and begins to write himself a note to jog his memory in anticipation of being subject to Laser-Guided Amnesia along with the implantation of a new personality as per the law. In looking for a place to hide the note, he realizes he already did this the first time he took the fall for the real murderer - he had nowhere else to hide the note but inside his own body, so he cut open the skin over his stomach and hid the note with a photo of the real murderer inside his own body.
ef - a tale of memories: Chihiro's memory only lasts for around 12 hours, so every night before she goes to bed she writes in a diary what she did that day, and every day when she wakes up she reads all the diary entries she's written to remind herself of her life.
Bella of the Alternate Universe FicLuminosity does this all the time. She would like to do it more, but before she meets vampires she doesn't just due to the practical fact that there's only so much time in the day, and after she meets vampires with ESP abilities she had to go to great lengths to keep her written thoughts private. This is one of her reasons for wanting to be a vampire: perfect memory.
In Came Out of the Darkness a note Fred left to himself broke a memory block on George and himself. (George was affected as well because as magical twins they had a soul bond.)
The main character from the original Total Recall (1990) used two video messages. These set up some of the best lines and scenes in the movie. Turns out that he came up with the plan and is manipulating himself with the clues he left behind to function as the perfect mole. It's not every day you Mind Screw yourself on purpose.
Done by the protagonist in the movie Memento, using pictures as well as tattooing information onto his skin.
He also only trusts notes to himself that are in his own handwriting. At one point another character insists that he write something down that he doesn't believe is true, so he purposely writes it in different handwriting so that he won't believe it when he reads it later.
Chris Pratt in The Lookout, who has a bad short-term memory due to a serious head injury and needs to write everything down just to get through the day.
In the film The Machinist, the main character unknowingly leaves post-it notes of a game of hangman to unearth the suppressed memory of his fatal hit-and-run.
In the film 50 First Dates, the main character Lucy keeps a journal (later a video tape) since she loses her memory every day.
One of the protagonist's envelopes in Push is addressed to himself.
Kira also leaves a short message for herself written in her lipstick on a mirror. She even checks to make sure it's her own handwriting.
In Bill And Ted's Excellent Adventure, the title characters find a note left by their future selves at the police station. More often, this trope is evoked throughout the movie in a fashion similar to the Norm MacDonald example above.
Similar to Memento and 50 First Dates, the Dana Carvey film Clean Slate is about a private investigator suffering from anterograde amnesia, using a tape recorder to leave himself notes.
In Looper, this happens twice. First, Old Joe pins a paper note on an unconscious Young Joe's jacket, warning him to skip town before the mob figures out he didn't kill his older self. Later, Young Joe carves the name of his favorite waitress into his arm. Old Joe reads the scars that appear on his arm and meets his younger self at the diner.
The protagonist of the novel The Raw Shark Texts finds one of these after waking up on his bathroom floor with absolutely no memory due to the memory-eating shark that has been hunting him.
Artemis Fowl puts together a slightly more complicated version of this (involving a video-message, among other things) as part of a Memory Gambit in his own book series after being mind-wiped in the third book. It comes to fruition in the fourth.
The protagonist of the 1952 short story (quite possibly making it the origin of this idea) and 2003 film Paycheck did this with a bag full of random items triggering a Gambit Roulette to act as the proof.
Tally Youngblood had to write her future self a note in Uglies, because after she underwent the traditional surgical procedure that made her a Pretty, she would forget all the plans she had made beforehand to eventually reverse the process.
Gene Wolfe's Soldier of the Mist and sequels are written as the journal of the hero, Latro, who has anterograde amnesia, constantly losing his memory of the previous day. The first words of the journal are "Read this each day."
Discworld: the Time Monks force Sam Vimes to do this to himself so they can tell him sensitive information without letting him remember it. Sam being who he is, he figures it out again anyway.
Real life example: in one of his early essays, David Sedaris talks about his first boy-crush attempting to out him at summer camp by showing off a note that he claimed to have found on David's bed. The note read, 'I like guys.' Present-day David speculates that presumably, the idea was that he'd written the note to himself, in case he somehow forgot that he was gay.
There's one SF short story where aliens steal all human memories - each night, those of one more day, going back in time. People have to employ this for a long time - more than a decade, in fact.
In the Piers Anthony novel "Politician" (part of the Bio of a Space Tyrant), Hope Hubris is mind-wiped right before the election for President. His captors try to plant false memories to discredit him since he would contradict statements he made during the campaign. He finds a set of coded words that trigger his real memories hidden under ...well, let's just say they kept him in a dark pit-like compartment for a long time and leave it at that. The coded words allow him to relive the experiences he had, but also cause him to relive the mental anguish of losing family members again.
This trope is the main premise of the novel The Rook
The backstory of one character in Dan Simmons' novel "Hyperion" involves a young woman who begins aging backward. Her memory keeps pace with the physical age of her brain, losing one day each day, so her letters to herself accumulate to quite a stack, until she realizes the futility of writing them.
The novel Turnabout features a group of elderly people who sign up for an experimental treatment to make them grow young again. After the process begins, they discover there's no way to stop the process...and each time they regress a year, they lose their memories of that year. The two main characters keep journals of everything they remember from a given year so that they can at least enjoy the stories as they regress to infancy.
Live Action TV
In the episode "The Storm Before the Calm" of Happy Endings, Dave is giving himself reminders on a tape recorder.
At the end of the episode, the gang yoinks his recorder away and plays it for their amusement.
Recorder!Dave: David, always remember don't call a person sailor unless you're absolutely positive that person's a sailor.
Max: Oh my gosh, you do that all the time, you do that all the time.
Recorder!Dave: Oh! new downstairs hair design idea-double lightning bolts. Win, win...On a personal note, I really love my friends...
Everybody: Ah, Dave.
Recorder!Dave: In the following order.
Daniel Faraday apparently did this at some point on LOST. He's surprised to find the note "If anything goes wrong, Desmond Hume will be my constant" in his journal.
It's later revealed that Daniel suffered from memory loss due to a botched time travel experiment, and his past self who wrote the journal knew about Desmond and the other information there due solely to the Stable Time Loop created in that episode.
Gwen Cooper in the first episode of Torchwood, but she wasn't as successful.
In Doctor Who series 6, when team TARDIS faces an alien that you can't remember the moment you look away, they leave notes to themselves (often all over their body) telling them what to do. Paranoia Fuel at its finest.
Even earlier, in "The Beast Below", Amy leaves a video recording for herself telling herself to get the Doctor off the ship after she learns about (and then erases her memories of) the Star Whale. Liz 10 leaves herself a recording in the same situation.
Bennett from Heroes leaves himself a note saying "Claire's safe. She's with friends." after he sends Claire away to keep her safe from the Company and has the Haitian wipe his mind of any memories that could possibly lead them to her. His wife gives him the note, telling him he wrote it.
Doesn't involve amnesia, but in How I Met Your Mother a Running Gag is that the characters occasionally write letters to themselves addressed 'Dear Future Ted' and signed 'Past Ted'. It also gives us this little gem :
Ted: That is a tough problem. You know who'd know how to solve that one?
Ted: Future Ted and Future Marshall.
Marshall: Yeah, let's just let those guys sort it out.
Two months later :
Marshall: Damn it, Past Marshall!
Ted has a habit of of writing letters to himself after his breakups so that in the future, if he is tempted to start dating one of his exes, he can go back to the letter and be reminded of why they broke up to avoid making the same mistake. Some of the previous episodes become Hilarious in Hindsight this revelation as Ted's first letter of this type is about Karen, the pretentious Jerk Ass and notorious cheater who was Ted's college girlfriend who he kept getting back together with, even after the relationship kept ending the same way.
Rodney McKay in Stargate Atlantis used a video message when everyone in Atlantis lost their memories in "Tabula Rasa."
In Stargate SG-1, Vala has her memory altered (so that she believes she was abandoned by SG1) in a batmanGambit to capture Adria. She leaves a Note to Self for after she is brought back, knowing she would be...rather upset with her teammates otherwise.
Another episode, 2010, taking place in the then-future year of 2010, showing that the Goa'uld have been defeated by a benevolent and powerful alien race that SG-1 discovered. It is later revealed that the aliens have used their technology to secretly sterilize humanity so they can take over when everyone has died of old age. Jack is able to use the Stargate to send a message back in time warning his past self not to go to the star where they discovered the aliens.General Hammondimmediately issues an order that the note's instructions be followed.
Star Trek: Voyager ("Unforgettable"). Chakotay falls in love with a beautiful alien from a species that fades from memory after a while. To ensure this they also implant a virus that destroys all computer records. To make sure he doesn't forget, Chakotay writes out what happened on paper.
Kurt Mendel in the Odyssey 5 episode "Time Out of Mind"
Upon waking up in Shibuya with Laser-Guided Amnesia, Tsuyoshi finds a note in his mouth written in blood that simply says, "LEAVE SHIBUYA. - RAVE". After the Restore, he pulls the same trick by swallowing one of Ema's fake fingernails, which is significantly more successful in jogging his memories.
In the episode of Loisand Clark:The New Adventuresof Superman, when Lois is in 1966 and finds out that Clark is Superman, she writes a note to herself when she finds out H.G. Wells will cause her to forget this. Luckily, Clark sees the note before she does and the secret is kept until later in the series.
The Troop: Gus once told the heroes they could erase his memory since he had hidden reminders. They instead sent him to a mental institution where his tales about monsters will be disregarded as delusions.
In the parody song 'bimbo nr 5' 'Bill Clinton' literally says 'note to myself, nail her later.'
In Liberty Meadows, a Running Gag punchline has a character recording a note to themselves via tape recorder. No amnesia is involved. It's just a reminder for the future.
Ralph: (after watching Dean get maced by yet another woman) "Note to self: buy stock in mace."
The Practical Incarnation in Planescape: Torment, upon learning that he would lose his memory upon death, set up several contingency plans (including keeping a journal and tattooing his own back with instructions) to make sure that future incarnations would be able to follow in his footsteps and finish his work. Unfortunately for both of you, by the time the current incarnation of the Nameless One comes around, some of the incarnations who've lived in-between (amongst them the Paranoid Incarnation) have ruined most of them.
They also left behind various body parts, including his eye and arm, and hid stuff for you in your intestines.
Amnesia: The Dark Descent starts with the player character waking up close to one of these, informing him that he wiped his own memory willingly, and now has to kill a certain baron of the castle he finds himself in.
In Little Busters, Kurugaya starts leaving notes to herself when she realises that, because the world they're in is breaking down, she is losing her memory of Riki trying (and succeeding) to ask her out. The jig is up when Riki discovers a note saying 'You're going out with Riki.'
In Freefall, as part of a series of tests, Florence (an uplifted red wolf) was injected with a chemical which prevented her short term memory from being converted into long term. When it was activated, she used a Post-It pad and pen to remind her where she was going, what she was doing, and even the fact that her memory was affected. Included in the notes was a note saying "skip to the end" because her memory was only about three minutes long, and reading all the notes she'd accumulated at that point would have taken too long.
At one point in Schlock Mercenary, when the entire crew was undergoing forced memory rewrites, Schlock used the properties of his Bizarre Alien Biology to store his real memories of the encounter inside a bit of himself, which he protected from the rewrite by shoving it inside one of his extra eyeballs. Schlock was smart enough to realize that he couldn't actually get the crew to remember what really happened—such an effort would most likely lead to them getting killed. Instead, he just made sure to tell himself to kill the bastard who did it to them.
Wapsi Square. Stuck in a time loop, Brandi writes a book to her future self detailing how to get out of the time loop.
Adam and Jamie in Irregular Webcomic! wrote to themselves to remind that Elvis Presley is alive before erasing excessive memories (including the info about Elvis) from when they drink from Mnemosyne river. Naturally, they don't believe it.
In Spacetrawler, Pierrot, upon learning that he's to be brain-wiped by the subterranean Mihrrgoots, writes himself a letter containing some very important information about the Eeb liberation mission he's on. After the mind-wipe, he finds the letter in his pocket... and he dismisses it, assuming that he just had too much to drink. Later, the letter ends up becoming important anyway—the king of the Mihrrgoots gains Pierrot's trust by referring to the contents of the letter.
Most characters in Ruby Quest, if not all, are suffering from amnesia, and at least two people have attempted to counter this by leaving notes to themselves: Tom discovers writing inside his locker, advising him not to trust #7, i.e. Ruby - the reason is revealed soon, and results in a temporary break-up between the two. Meanwhile, the head doctor, Filbert, wrote a note that simply told that he has amnesia, which is why he can't remember things - as well as ensuring him that he is still clean.
A kid who saw the first contact between humans and aliens in the Men in Black cartoon series. Also, Jay warning his past self not to use an invention that'd eventually made his head explode.
On The Angry Beavers, Norbert recorded a tape telling himself how to regain his memories under the Genre Savvy presumption that he'd eventually be hit on the head by his accident-prone brother and get amnesia. It even contained a Shout-Out to Total Recall. His solution? Just let his brother hit him on the head again.
At the end of the Invader Zim episode "Bad, Bad Rubber Piggy", Zim desperately throws a note into his time machine and back into the past after severely screwing up the timeline. This somewhat works as the note switches places with his brain, leaving him a drooling moron holding a brain (and thus repairing the timeline). What it said? "ZIM, DON'T USE THE TIME MACHINE! LOVE, ZIM!"
Cruella de Vil on the 101 Dalmatians cartoon would make these, despite never actually having lost her memory (well, except that one time).
The Histeria!! version of Christopher Columbus wrote one: "Never again hire anyone from Cabin Crews R Us."
Generator Rex: Rex suffers from chronic amnesia (as in he'll suddenly blackout and forget everything about his life up to that point.) During one of his "lives", he compensates by making a comprehensive journal for this purpose. However, Rex destroyed the journal upon realizing what an ass that past self was, though he's since started a new one.
Hank makes a video note in The Venture Bros. when he has to have his memory erased after he sleeps with a woman, finally losing his virginity, only to discover that the woman was the mother of his best friend Dermott... and that his own father, Dr. Venture, was Dermott's actual father. Hank's note to self is something where he reassures himself that he got laid.
Phineas and Ferb: Doofenshmirtz once turned Perry the Platypus into his butler. Before being brainwashed, Perry wrote to himself a reminder on his chest that, when reflected on a mirror, read "I fight evil".
Penelope to her past self in Atomic Betty episode "The Future is Now". Past!Penelope didn't believe.