Variation: thanks to The Nth Doctor, there's currently thirteennote counting the War Doctor different incarnations of the Doctor running around the space/time... it's extremely rare for them to meet (Timey-Wimey Ball, actors dying and all that), but when they do the result tends to be similar to this trope. The 10 Doctors is an artist's rendition, shall we say, of how the first ten Doctors would act if forced to cooperate.
A straight example in "The End of Time": The Master hijacks the Immortality Gate to transform the entire human race except for Wilf note (locked in a radiation-shielded room) and Donna note (thanks to the events of "Journey's End" making her half-Time Lord) into "The Master Race", a planet-wide population of (insane, madly laughing) Master copies.
Also in "The Deadly Assassin", while in the Matrix, the assassin takes on various generic historical personas (a samurai, a clown, a WW1 biplane pilot, etc.) to attack/frighten the Doctor (and the audience). At one point several of him seem to man several positions on a train (or trains) simultaneously to run over the Doctor's leg.
In another Fourth Doctor story, "The Leisure Hive", the villain Pangol used a form of Applied Phlebotinum to recreate himself thousands of times over as a conquering army. Thanks to the Doctor's interference he ended up with an army of Doctors, which disintegrated within minutes of their generation.
An arc in the later seasons of Stargate SG-1 had Baal make dozens of clones of himself, and in a few episodes set on Earth at least five of them hung out together. One episode even has a Gotta Catch Them All where the heroes travel the galaxy, trying to scoop up all the Baal clones. A freeze frame near the end of the episode shows fifteen clones in one room. It turns out it was a Batman Gambit. Baal knew the heroes would give him the info he wanted to buy time when he had hostages, as long as they knew he couldn't escape with that info. And the clones? Each one has a transponder, too weak to be detected, but if they all stand in one place...
The Monster of the Week of an episode of Power Rangers Dino Thunder had the power to create copies of anything in front of him. At one point, he made three copies of Cassidy on the spot, and the four of them proceeded to drive Devin crazy by stacking him with chores.
An episode of Eureka features Dr. Stark accidentally cloning himself. The clones try to take over the world. Long story.
Round the Twist has a character make only one clone to win a running competition. However, a rabbit starts cloning an army of itself with the machine. All the objects used in the machine, cloned or original, begin to dissolve eventually, due to a fault in the machine. At least one rabbit survives, though, because in the final scene we learn what happened when Bronson put her with a male rabbit.
In Game of Thrones the warlock Pyatt Pree appears to create a double of himself, although many of those watching think the warlocks are charlatans and this is just a trick. It's revealed in the next episode that he really can do this, and create more than a single copy too.
In the episode "Which Prue is it Anyway?", Prue decides she needs a power boost, and casts a spell to triple her power. Unfortunately, she doesn't realize that what it actually does is create three of her. It turns out to be useful, after all, because the two clones end up dying instead of the original Prue.
When Piper finds out that the Angel of Death is after her husband Leo in the episode "Vaya con Leos", she decides to cast a spell to hide him. While the spell does confuse the Angel of Death, it had an unintended effect: every man in San Francisco got turned into a clone of Leo.