Gwen Tennyson (Ben 10) going to Ledgerdomain the realm of magic.
Catbug (Bravest Warriors) midway through jumping into the See-Through Zone.
As a Archai, Tyler Michaels (Charmed comic) has the ability to create portals to other worlds, dimensions or planes by burning holes in reality.
The Fenton Ghost Portal (Danny Phantom) allows access to the Ghost Zone.
The Infi-Map can travel between the Ghost Zone and the Human World.
Wulf (Danny Phantom) can use his claws to rip open portals between Earth and the Ghost Zone.
Zandora's Box (Dungeons & Dragons: The Animation) can lead to any possible and impossible dimension, depending on where its opened.
Breach (Generator Rex) using her extra arms to open dimensional portals.
Grim (The Grim Adventures of Billy and Mandy) can use his scythe to slash open dimensional portals.
The Dimensional Scissors (Star vs. the Forces of Evil) are magical scissors that can cut open portals to other dimensions.
Hekapoo (Star vs. the Forces of Evil) the creator of the dimensional scissors.
Interdimensional Portal (The Jimmy Timmy Power Hour III: The Jerkinators!)
Porta-Portal (The Jimmy Timmy Power Hour III: The Jerkinators!)
Uncle Grandpa (Uncle Grandpa), among many other amazing abilities, can travel through various dimensions and planes of existence, and can even travel into other cartoon-universes as seen in the "Steven Universe" crossover.
The Magical Watches (Winx Club) can open portals to the World of Dreams/Neverland.
Combo Man (Marvel Comics) possesses The Century's dimensional travel.
America Chavez (Marvel Comics)
The Heart of Etheria (She-Ra and the Princesses of Power) can transport entire planets to other dimensions.