Sure to be spoilers here, and I haven't even finished the game yet.

Found a pretty big one after playing that snake game in Ranger Citadel. A file is created in your documents folder, under "Drive1". Open it a text editor.... Wow!

I'm sure there are many relating to Fallout and the first Wasteland game too, but as I didn't play those I wouldn't really know about them, other than catching the Vault #13 thing. The Bloodstaff in the museum sounded like a big deal, but I wouldn't know about its significance.

One that genuinly made me laugh out loud was about Johnny Cash. "So you're the boy named Sue?" or something to that effect. Hilarious :D

Also liked the Gandhi quote at a Mysterious Shrine. One of my heroes.

Perhaps this is stretching it too much, but as I approached that Shrine, I wondered if it was a reference to 2001: A space odyssey.

There was something about Dr Strangelove somewhere too, probably in relation to those wacko Mushroom Cloud guys, but I don't recall exactly where I saw it.

I'm sure there are loads of others too.