Spoofed on Homestar Runner in the Strong Bad Email "cliffhangers", where Strong Bad is asked by a fan to "Resolve all the cliffhangers, please". Of course, none of the cartoons on the site had cliffhangers, so Strong Bad has to improvise. After showing three mock cliffhangers involving the Thinkkaman, Strong Bad as Space Captainface, and Homestar being pregnant, which are each resolved shortly after they begin (Coach Z fails to unmask the Thinkkaman because he slips which allows the Thinkkaman to escape, Cap stumbles across a fruit system rather than a comet, and Strong Sad points out to Homestar that he can’t be pregnant because he's male), the email ends on an actual cliffhanger when Strong Bad's Lappy 486 computer gets stolen.
Episode 17 ends in the Inquisition charging into the Eternity Hall and "recognizing" Magnus as a villain, with the stalemate being resolved in the next episode.
Season two ends with the Centurion revealing himself to be Rogal Dorn, to the shock of all present.
Matthew Santoro: At the end of THE GREATEST EVAR!, Hugo knocks Matt unconscious and takes over Matt's web series. This doesn't get resolved until the next episode, Drake NYC Riot!, when Matt gets his web series back.
The online novel The Saga of Tuck has (for now) 142 chapters, each almost always ending on a cliff hanger.
Red vs. Blue does this very often with its season finales:
Season 1: Caboose changes voices and starts calling himself O'Malley. This is later revealed to be Caboose being hijacked by the AI known as Omega.
Season 2: The Reds and Blues team up to stop Omega only to scattered around the galaxy due to a teleporter malfunction. Also, Tex recognizes Donut as the one who killed her.
Season 3: The Reds find themselves back in Blood Gulch, and Church is about to be attacked by an alien.
Season 8: Church traps himself in Epsilon in an attempt to bring Tex back.
Season 9: Carolina is revealed to be alive, and asks for the Reds and Blues to help her kill the Director.
Season 11: Tucker, Grif, Simmons, and Caboose join the New Republic to rescue their captured friends.
Season 13: A Bolivian Army Ending, ending with Church sacrificing himself to help the Reds and Blues hopefully get out alive.
Wildbow, the author of Pact and Worm, is especially fond of these - he subscribes to the belief that continued tension is necessary to keep readers following his work, which is published in serial format, so he will more often than not end a chapter on a cliffhanger of some sort, including the introduction of a new enemy, a sudden turn of fortunes for the protagonists, or when all else fails, mysterious hinting at an Unspoken Plan Guarantee. He has, on occasion, ended a chapter mid-sentence.
Unresolved Cliffhangers:
The season finale of Brains has Alison grabbing her camera and running from the murderer Professor Sherman.
David Near: At the end of the Sally Williams video, after Sally kills her uncle, she hears a loud thud and says "Wh-What was that?" Then "Pop Goes The Weasel" starts to play and a familiar cackle can be heard...
Dusk's Dawn: We never see what happened to the antagonist, or when the protagonists went to Celestia.
Gotham: The Series ends with Richard's mother, Elizabeth, attending the Nicole Miller fashion show and passing out leaving Catherine to call Richard to tell him that Elizabeth was rushed to the hospital. Elizabeth's fate is unknown. The series doesn't look like it's going to continue despite an Emmy nomination.
Return of the Cartoon Man ends with Roy and Valerie crossing into the Second Dimension to save Karen from Simon, along with a tease of Oswald Sherzikien's master plan, which supposedly affects the entire world. Expected to be resolved in the follow-up Journey of the Cartoon Man.
SSBMEXPERT's YouTube Poop, Oh Ship! - Part 1 had Mario and Luigi going on a mission to rescue King Harkinian and Hyrule Castle from a washout, which leads to a police chase, but due to SSBMEXPERT going inactive (before deleting his account near the end of the 2010s), we will never get to see it concluded.
" ends with Nick telling the audience to tune in next time for their game on Mario Party 2's Bowser Land, which wouldn't be uploaded on Brent's channel as "Mario Party 2 Bowser Land is WAY too toxic...