Ah! I can't believe I forgot to mention this!
I'd lovelovelovelovelove a game based on Susanna Clarke's Jonathan Strange & Mr. Norrell and The Ladies of Grace Adieu.
And as cliche as it sounds, a Sin City game wouldn't be remiss either.
In the "that game already exists" department, using Mage: the Awakening and Changeling: the Dreaming together would be a perfect fit for the Jonathan Strange-verse. They even reference Clarke's novel as an inspiration source at the beginning of Changeling. Little to no adaptation would be needed at all, just a few setting-specific items. Hell, Mage and Changeling combined would be
Jonathan Strange and Mr. Norrell. The universes work in similar ways, you're just setting it during a historical period rather than present day, and scrubbing Atlantis references from the magic (which many seem to do anyway.)
You could do the Dresden Files with new World of Darkness pretty easily, as well.
Mage would also cover the Night Watch series by Sergei Lukyanenko very well with few changes. (I highly recommend these books to people who like books of modern magic / fantasy.)
I once did a Mutants and Masterminds conversion for the Matrix films (before I got disgusted with the whole thing after the third movie and Matrix Online): identifying which powers were available, creating powers for moves and tricks performed, coming up with stats for exiles and agents, and rules for jacking in and jacking out as well as the uploading of skills and abilities. I wish I still had the file, it could come in handy for other stuff.
I once thought about running a Spycraft campaign in the
Alias universe.
The Farscape RPG was abysmal, and I once considered "fixing" it.
I agree completely about Fallout. I'm having a lot of fun playing it through a second time (and probably a third.)
I've considered adapting the plot of Bioshock into a series of adventures for an RPG. Or System Shock 2. Or using Bioshock just as a basis, even with D&D (a wizard with an Objectivist ideal of morality decides to create his own undersea kingdom that devolves into anarchy and chaos.)
The Thief: the Dark Project / Metal Age would be an excellent basis for a
campaign setting for an existing fantasy game.