Io

Io is a moon of Jupiter. In real life, it is notable for its sulphur volcanoes. In the Transformers universe, however, it is the home of psychotic alien bats that transform into missiles.

Cartoon continuity
Blurr and Wheelie crashed on Io while delivering Metroplex's transformation cog to Earth, where they were attacked by the local wildlife. They were soon joined by Marissa Faireborne, courtesy of the locals' skills as kamekaze pilots. All three had to be rescued by the Autobots' current ride.

Chip and Dale Rescue Rangers
in Katy meets the Aliens, Professor Norton Nimnul discovers Aliens W, X, Y and Z on Io, who four aliens are hungry and the only way to survive is to capture and eat creatures from other planets.

Exosquad
Io, the innermost of Jupiter's Galilean moons, served as temporary base for Admiral Winfield's Exofleet remnant in the first years of the Neosapien War. It became a critical base after the destruction of the Resolute and much of Exofleet during the Third Battle of Earth.

During the Blockade of Io, the Neosapien fleet placed Io under seige due to the belief that Winfield had a functioning GRAF Shield. When Typhonus learned that the shield was non-operational, he ordered a full scale attack. However, the Pirate Clans came to Exofleet's aid and inflicted heavy losses on his fleet.

Combined with the losses he had suffered from the aftermath of the Battle of Sinope, Typhonus chose to retreat. This allowed Exofleet to escape to Chaos. Although Io was later captured by Typhonus, it was never mentioned again as a vital location until in Titan A.E., the base was destroyed by the Drej and Io was abandoned.