Recently, watching those Portal 2 trailers/previews got me thinking: "I could sure go for some Paranoia right now." You know, Paranoia, the game where The Computer controls everything, and is your friend, and where you could easily die due to your own stupidity (you should have known that that corridor was full of invisible lasers) or as just one subject in The Computer's experiments.
The first edition was published in Nineteen Eighty-Four.
I realized that people who liked Portal would probably like Paranoia, as far as RPGs go. Admittedly, if they don't already play RPGs, then Paranoia is probably a bad introduction to them, seeing as how knowing the rules is treason, but that's beside the point.
Anyway, that got me thinking: Given a video game, what RPG would a person who likes that probably also like?
If you liked Portal, then you'll love Paranoia.
If you liked DDO, then you'll love D&D 3.5.
That's all that I've got so far. I'm working on a list, which you can find here. If you have suggestions for VGs that I forgot, RPGs that I forgot, connections that I missed or didn't do justice, or whatever, then leave a comment below, send me an e-mail, or hit me up on twitter.