One-Wheeled Wonder

A character who moves by balancing on one wheel or ball.

There are three subtypes:

Integrated unicycle: A character, usually a robot or Powered Armor, has a wheel at the bottom and a center of mass above the wheel.
Separate unicycle: The character is frequently or always riding a vehicle with one wheel.
Wheel is most of body: Center of mass is within the wheel, as if a separate unicycle were autonomous.

It doesn't include characters that move by rolling or spin-dashing. See also Monowheel Mayhem for riding inside the wheel.

Examples of One-Wheeled Wonder include:

Anime and Manga

Venus Wars has Battle Biking, a violet sport, that uses one-wheeled monobikes for a roller derby-ish fighting sport. The Killer Commandos, the team that the heroes are on, uses their bikes for to fight against Ishtar invaders.
Victory Gundam has the Einerad, which is nothing more than a wheel with a pair of cannons, a missile launcher and a place for a mobile suit to stand mounted on the unmoving center with no clear way for the driver to actually see in front of him. This is a series where everyone can fly. While the claim that Victory had intentionally stupid looking things as a jab against To Sell Toys executives remains unproven, it would certainly explain the Einerad.
- Gundam Build Fighters's Ricardo Fellini, who sometimes uses the Meteor Hopper, a one-wheeled motorcycle for his Wing Gundam Fenice. After upgrading his Gundam to transform, he quits using this motorcycle.
Dragon Ball has Launch using a one-wheeled bike to rob a train in her first episode appearance.

Star Wars: Dark Empire 2: Empatojayos Brand is a Jedi Knight, whose prosthetic arms and robotic torso give him a spherical shape.

Officer Shrift in the animated version of The Phantom Tollbooth. who uses a wheel that resembles a rolling chair, it's connected to a car jack device that can be raised just to aid with his height. Unknown if this is a separate vehicle that he uses or a part of him.
M-O in WALL-E
The non-evil characters in Poet Anderson: The Dream Walker use one wheeled hoverbikes.

WA-7 in Attack of the Clones, who are droid waitresses that balanced on a single wheel. They can be found in Dexter's Diner.
- BB-8 from the final trilogy, although rather than a wheel he uses a sphere.
In Spy Kids 3, one of the Mega Race bikes is a motorized unicycle and high seat.

The aptly named "Wheelers" creatures from the original Oz books, they have wheels instead of hands and feet.
In Ciaphas Cain, one of the techpriests had his lower body replaced with a single wheel. Worst is that the techpriests love to replace their bodies with metal and they have metal dendrites to help them with this, though he must gotten really good gyroscopes to work.
In the third book of His Dark Materials, there's a race of Starfish Aliens called the Mulefa that uses a round seed as a wheel. They attach it with their two middle feet.

Both the Tokusou Sentai Dekaranger and Power Rangers S.P.D. (its American cousin) has the DekaBreak/Omega Range, whose personal vehicle is a one-wheeled motorcycle.

The Youkai, Wa-nyūdō, who is a giant that has his/her head trapped within an ox-cart wheel, which is flaming.

Robots in Ball Breakers
Claptrap in Borderlands
Gilliam Knight in Mega Man 7
Maestro Trombot in JumpStart Adventures 3rd Grade: Mystery Mountain
The Mcycle body shape in Cyber Stadium Series: Base Wars
Medic Robot in Team Fortress 2
Mettaton in Undertale.
PDQ-88b securitron in Fallout: New Vegas.
Roadkill Rodney with the electroshock whip in Teenage Mutant Ninja Turtles II: The Arcade Game
Rocket in Rocket: Robot on Wheels
Robo-Ninja in Robo-Ninja Climb
Wheelie in Kirby Super Star has the wheel as most of body variant and becomes the vehicle variant when Kirby is riding him.
- Several types of Wheelie Bike exist in Air Ride. They share several unusual characteristics separate from the rest of the, otherwise hovercraft, vehicle options.

Boybot from Cyanide & Happiness #2638 is an android with a wheel at the bottom who scares off one woman and dates the other.

The Gizmoduck powered armor worn by Fenton Crackshell in DuckTales and Darkwing Duck
Solenoid robots in Roger Ramjet.
The Ruff & Reddy Show has the Muni Mula men, who balance on a single wheel.
The Zone Rider, a one-wheeled motorcycles that are used by Zone Riders.
Buzz Lightyear of Star Command's final episode introduces a robot personality love interest for XR. Her name is 42; at the end of the episode, 42's personality was removed "surgically" and placed into a short, humanoid, robotic body which has a single wheel it uses to get around.
In Legends of Chima, some of the Speedors use one-wheeled vehicles in their races.

The Robotpark has a wiki (which also doubles as the World's Largest Robot Resource) with a page about single wheel/ball robots.
Mainly the unicycle.
A self-propelled unicycle was developed. Similar to the Segway, the rider has to do is lean forward.
The first fully functional one wheeled-motorcycle, called the Uno-Wheel Motorcycle. Basically, it has two wheels that are side-by-side, appearing similar to Code Lyoko's Overbike.