Sliders
Stargate
Warcraft dark portal
Diablo town portal
Portal game (duh)
Rick & Morty
List of fiction employing parallel universes
Portals, Authored by: Jennifer Harwood-Smith, The Routledge Companion to Imaginary Worlds
Exploring the Four Types of Portal Narratives
From Wonderland to Outlander, Your Guide to Portals to Other Worlds
Lev Grossman lists his 5 favorite magic portals in fantasy fiction
First instances of portal for each media type: The Blazing World?