Dungeons and Dragons meets Stargate SG-1: A scientific team discovers a device that they believe allows for instant interstellar
travel but that really allows travel to other dimensions including some full of evil creatures. These destinations are what
lead to an ongoing conflict.
(A variation on this idea simply uses a variety of settings from the books Manual of the Planes and Beyond Countless
Doorways as the sites of various adventures.)
Diablo II in Manhattan - The Prime Evils from the famous PC games turn their attention to 21st century Earth. The good
guys discover one of the demons' scouting missions and the battle to stop a full-scale invasion is on!
Post-Apocalypse Diablo - A mgaical cataclysm has destroyed most of civilization and changed the laws of physics. The
heroes, their high-tech weapons and electronics now useless, have to stop the demonic invasion.
The Day the World Changed - This is the same magical cataclysm mentioned above, but without all of the drama. The residents
of a small, isolated town try to cope with the inevitable unravelling of civilization that comes when most our high-tech devices
mysteriously stop working. Some weak supernatural abilities and some mutant animals appear but are not central to the story.
The Day the Earth Died - A nearby star has begun emitting gamma ray bursts that will render the earth's surface uninhabitable.
The characters are trying to organize efforts to create a new, underground civilization. Picture "The Day After Tomorrow"
and "The West Wing".
Robotech - Making the cheesy kid's cartoons into an adult drama, live action at that. I would lose the destroids, transforming
spacecraft, and 50-foot aliens (make 'em normal sized!) and make the Earth aircraft a little more futuristic.
Chronicles of the Galactic Lensmen - TV series that eliminates some of the technobabble (macrobeams, dirigible ball lightning),
updates the anachronistic technology (e.g. switchboards and typewriters), and makes the aliens more alien.