Turns out Stan Lee has a LONG history of cameos dating back 30-40 years.
Spider-Man and His Amazing Friends - 7 Little Superheroes [S1 Ep6] (October 1981)
While not technically a cameo, Stan Lee narrated an episode of the animated series Spider-Man and His Amazing Friends in 1981.
The Trial of the Incredible Hulk (May 1989)
Stan Lee's first live-action cameo is in a TV film based on the 1978 Incredible Hulk TV show. Bruce Banner is wrongly on trial for sexual assault and is being defended in court by Matt Murdock (Daredevil).
Stan appears as a jury member when Hulk transforms and tears the room apart.
Jim Henson's Muppet Babies - Comic Capers [S6 Ep6] (October 1989)
Appears as himself alongside Spider-Man.
Mallrats (October 1995)
Stan Lee gives romantic advice in what is supposedly his favorite movie appearance of all time.
Spider-Man: The Animated Series - Spider-Wars Part 2 [S5 Ep13] (January 1998)
In the show's final episode, Spider-Man travels to a dimension where he is a fictional superhero and Stan Lee is his creator. He uses his webslingers to give Stan a ride around town and chat before leaving him on top of a building and returning to his own universe.
Superman: The Animated Series - Apokolips... Now! Part 2 [S2 Ep26] (February 1998)
Yes, you read that correctly.
In the episode's original TV broadcast, Dan Turpin's funeral contained cameos from multiple Marvel characters and employees, including Captain America, Tony Stark, Nick Fury, and of course, Stan Lee. These cameos were removed for the episode's DVD release.
X-Men (July 2000)
Stan Lee plays a hot dog vendor seen after Senator Robert Kelly emerges from the sea after escaping Magneto.
The Simpsons - I Am Furious (Yellow) [S13 Ep18] (April 2002)
Spider-Man (May 2002)
Lee saves a young girl from falling debris during Spider-Man's fight with the Green Goblin.
In a deleted scene, he also plays a street vendor who tries to sell Peter Parker a pair of sunglasses.
Daredevil (February 2003)
In a deleted scene, a young Matt Murdock saves an oblivious Stan Lee from walking into traffic.
Hulk (June 2003)
In his first live-action speaking role, Stan Lee plays a security guard talking with Hulk's original TV actor Lou Ferrigno.
Spider-Man 2 (June 2004)
Stan Lee once again plays a random bystander. This time, he saves a woman from being crushed by rubble while Spider-Man fights Doctor Octopus.
In a deleted scene, Lee has another cameo, saying "Look, Spider-Man stole that kid's sneakers."
The Princess Diaries 2: Royal Engagement (August 2004)
If you're going to ask why Stan Lee is in Princess Diaries 2, someone's already asked that question for you.
The answer? We have no idea.
Man-Thing (April 2005)
A photo of Stan Lee is seen on a board of missing people.
Fantastic Four (July 2005)
Stan Lee plays Reed Richards' mailman, Willie Lumpkin.
X-Men: The Last Stand (May 2006)
Jean Grey's powers affects gravity in the surrounding area, including Stan Lee's garden hose.
Heroes - Unexpected [S1 Ep16] (February 2007)
Stan Lee plays a truck driver.
Spider-Man 3 (April 2007)
While looking at a sign reading 'Spider-man To Receive Key To The City', Stan tells Peter Parker, "You know, I guess one person can make a difference... Nuff said."
Robot Chicken - Tapping a Hero [S3 Ep4] (September 2007)
Fantastic Four: Rise of the Silver Surfer (June 2007)
Stan tries to attend Reed Richards and Sue Storm's wedding, but is turned away when the bouncer doesn't believe him when he says he's Stan Lee.
Iron Man (May 2008)
Tony Stark mistakes Stan Lee for Hugh Hefner at a party.
In an alternate version of the scene, Lee replies "That's okay, I get this all the time."
The Incredible Hulk (June 2008)
Dies after being poisoned by green soda containing Bruce Banner's blood.
The Big Bang Theory - The Excelsior Acquisition [S3 Ep16] (March 2010)
Not only did Stan Lee cameo in an anime he helped write, he managed to create a brand new meme in the process.
Iron Man 2 (May 2010)
In a callback to Iron Man 1, Tony Stark mistakes Stan Lee for Larry King at a party.
Nikita - The Guardian [S1 Ep5] (October 2010)
Appears as Hank Excelsior, witness to a bank robbery who is interviewed by a TV reporter.
Pizza Man (2011)
Appears as himself in a cameo so obscure, I couldn't find what month the film was released.
Thor (May 2011)
"Stan the Man" unsuccessfully tries to move Thor's hammer with his pickup truck.
Captain America: The First Avenger (July 2011)
An elderly general who mistakes a another man for Captain America/Steve Rogers, commenting "I thought he'd be taller."
The Avengers (May 2012)
After the battle of New York City, Stan Lee is seen on TV playing chess as part of an interview. He dismisses the idea of super heroes existing in New York.
Stan Lee also appears in a deleted scene where he encourages Steve Rogers to ask a waitress for her number.
Ultimate Spider-Man - Great Power [S1 Ep1] (April 2012)
According to the Ultimate Spider-Man Wiki, Stan Lee has appeared in no less than 13 episodes of Ultimate Spider-Man as Stan the Janitor. He is secretly one of the original members of S.H.I.E.L.D.
Robot Chicken - Executed by the State [S6 Ep1] (September 2012)
Play as Stan Lee and use Spider-Man's web slinging powers to track down the missing pages for Stan's latest comic book script.
The Amazing Spider-Man (July 2012)
An unobservant librarian at the Midtown Science High School listening to music as Spider-Man fights The Lizard Dr. Curt Connors in the background.
Robot Chicken - Robot Fight Accident [S6 Ep18] (February 2013)
Iron Man 3 (May 2013)
Beauty pageant judge on TV who happily gives one of the contestants a 10.
Phineas and Ferb - Mission Marvel [S4 Ep16 & 17] (August 2013)
Thor: The Dark World (November 2013)
Lee appears as a mental ward patient who loans his shoe to Erik Selvig for a demonstration about "the Convergence" in his delusions. When Selvig finishes and asks if anyone has questions, Lee says, "Yeah, can I have my shoe back"?
The Simpsons - Married to the Blob [S25 Ep10] (January 2014)
Agents of S.H.I.E.L.D. - T.R.A.C.K.S. [S1 Ep13] (February 2014)
Captain America: The Winter Soldier (April 2014)
Lee plays a security guard at the Smithsonian Institution who after discovering that Captain America stole his own World War II uniform from an exhibit, says, "Oh man, I am so fired."
The Amazing Spider-Man 2 (May 2014)
A guest at Peter Parker and Gwen Stacy's graduation. Mentions that he recognises Peter Parker.
The Amazing Spider-Man 2 (Video Game) (May 2014)
One mission has Spider-Man saving Stan Lee from a burning building, followed by a visit to his comic book shop.
Guardians of the Galaxy (August 2014)
Rocket Racoon notices Stan flirting with alien women on Xandar.
Big Hero 6 (November 2014)
Revealed to be Fred's father in a post-credits scene.
Agent Carter - The Blitzkrieg Button [S1 Ep4] (January 2015)
Has his shoes shined while sitting next to Howard Stark.
Daredevil [S1 Ep13 & S2 Ep2]/Jessica Jones [S1 Ep7]/Luke Cage [S1 Ep12]/Iron Fist [S1 Ep13] (April 2015 to Present)
Senior NYPD officer Irving Forbush. He has appeared on an NYPD poster in every Netflix MCU series to date.
Avengers: Age of Ultron (May 2015)
Appears as a military veteran at the Avengers' victory party. He claims he fought at Omaha Beach and that it proves he can handle a shot of Asgardian liquor from Thor, but is then carried away drunk, muttering his catchphrase, "Excelsior!"
Ant Man (July 2015)
Bartender seen during Luis' flashback of Falcon looking for Ant-Man in a post-credits scene.
Lego Marvel's Avengers (January 2016)
Yoga Hosers (January 2016)
Appears as a police officer.
Stan Lee's Lucky Man - More Yang Than Yin [S1 Ep1] (January 2016)
Appears as himself signing autographs.
Deadpool (February 2016)
Stan appears as a strip club D.J. in the nightclub where Wade Wilson's/Deadpool's girlfriend Vanessa works.
Captain America: Civil War (April 2016)
FedEx delivery man asking mistaking Tony Stark for "Tony Stank".
X-Men: Apocalypse (May 2016)
Lee is shown viewing the rising nuclear weapons launched by Apocalypse next to his wife Joan.
Doctor Strange (October 2016)
Bus passenger reading The Doors of Perception by Aldous Huxley.
Logan (March 2017)/Deadpool 2 'No Good Deed' Teaser
In a teaser for Deadpool 2 that played before Logan (2017), Deadpool tells Stan Lee to shut up after being complimented on his superhero costume.
The Simpsons - The Caper Chase [S28 Ep18] (April 2017)
Stan Lee makes a brief cameo in the opening couch gag.
Guardians of the Galaxy Vol. 2 (May 2017)
Appears as an informant to the Watchers.
Fun bonus video: Stan Lee's Cameo School
I'm sure I've missed at least a few cameos. (The guy has freaking 106 actor credits on IMDB). Feel free to edit in any I've missed.