Cowboy Bebop at His Computer: A rather hilarious example, as some dubious journalists saw a Fallout 3 promo shot of a ruined Washington, D.C., without a watermark and assumed it was created by terrorists as a warning. Seriously.
The Citadel is the ruins of The Pentagon which serves as the headquarters of the Capital Wasteland Brotherhood of Steel. There's also the the Combine facility.
The Pitt is what used to be the city of Pittsburgh. The Pit is a stage in Mortal Kombat in which you can knock the opponent onto a bed of spikes, the hard stone floor, or a mass of spinning blades. This Pit is a winged warrior gunning for Medusa.
They have since been put back on Steam, with Bethesda now the publisher of these games in Interplay's place. It remains to be seen if they will return to GOG.
What Could Have Been: Originally, Fallout was going to be based on a licensed version of the paper RPG GURPS, from Steve Jackson Games, and would have published under the name Vault 13: A GURPS Post-Nuclear Adventure. But due to disagreements, including Steve Jackson disliking the appearance of Vault Boy on the character creation screen, and the execution of the insurgent from the intro, the deal was called off. Instead, Black Isle thought up the SPECIAL system, which has been used in every Fallout game ever since.
Word of Dante: The Fallout bibles put together by Chris Avellone.