I'm currently running a Red Markets inspired game in FATE Core. The previous campaign that I did was a Dreamlands/Inception mashup where the PCs were "interpretation analysts" hired by a tech startup that had this dream-decoding technology. Stuff currently rattling around the brainpan...
The Anarchy. One of my players really really REALLY wants to finally play a medieval-fantasy sort of game. So I tossed out an idea I'd had for a campaign based on the period in England called
the Anarchy. (Heavy inspiration from Pillars of the Earth/World Without End.) Haven't figured out what system I want to use, though.
Jagged Alliance. A scenario based on the old Jagged Alliance games: a team of mercenaries goes into a small Caribbean country to lead a revolt and overthrow the repressive government. I'm thinking of making the enemies double-extra-weird--a cross between African warlords and bad guys from Metal Gear games. I'm also unsure about what system I want to use for this, since it really cries out for some tactical gunz action. GURPs would probably do well, but I don't own it and have never played it. Savage Worlds is the other candidate, which would be less crunchy but is already on my bookshelf.
Werewolf Women of the SS. I want to do this as a Savage Worlds one-shot. That is all.
Lover in the Ice. One of my players keeps bugging me to do this game. The challenge is, he's already familiar with how it ends. The rest of the group has no idea...
Welcome to Weyland-Yutani. This is more a concept than a scenario so far. Basically, I want to surprise my players with the reveal that they're in the Alien/Aliens universe. If I start the game out with "so, you're on the Weyland-Yutani ship
Edmund Fitzgerald," then everyone's going to expect facehuggers and Gigermorphs. But if I just tell them they're playing a cyberpunk game, or a Resident-Evil-style survival horror game, I might be able to really surprise them.
Look Away, Dixie Land. I actually already ran this for my group. It's heavily inspired by the David Drake story, "Than Curse the Darkness," moved to the US South. The first version was set during the Civil War, but I might move it to the 1920s. The central idea is kind of a fake-out where you have the creepy white Southern family with the mysterious uncle who traveled the Dark Continent and brought back stuff...but the mythos villain is actually a cult of vengeful African-Americans, driven to extremism. Part of the fake-out is the reveal that one of the wealthy whites is a
Delphine LaLaurie inspired serial killer. I love the idea that the PCs discover the hidden torture chamber under the mansion...and it's not actually where the mythos magic is happening.
Edit:
Vikings! Between watching a documentary about a mass grave of beheaded Vikings in England, and the History channel series, I've been cultivating this nugget of an idea. Vikings land on England to pillage, run afoul of Glaaki's minions. And...uh, that's as far as I've gotten.