Cafe of Broken Dreams with characters that never made it into Fallout 3. Or some characters from Fallout 3, like when they had Tandi as her young self.(I generally hate people who cling to FO3 and want characters from that game but it would also be a reference to Fallout 2 so why not?)
I think I heard an earlier idea that had a diner appear in the middle of a sand storm, and when you walk into it, you see a couple of people all sitting in a booth talking, when you get close to them you see the Vault Dweller, the Lone Wanderer, and all the ''player characters'' from the Fallout games previous, and they all have blank faces (i.e. you really can't tell what they look like), and they're all talking about what they accomplished, what they did, then one hands you a drink and they all encourage you to drink it, so you do, and they continue to talk, and eventually they all look at you, and the Lone Wanderer (known so by the Vault 101 jumpsuit he/she/it would be wearing) turns to you and says ''So, Courier, what will you accomplish? Will you be a force for good, or serve evil? Who will you help? Will you accomplish as much as we have? Then you pass out (probably because of that drink), and when you wake up, you're in the middle of nowhere, no diner at all, but a special item would be sitting next to you. (maybe a unique weapon or special item that helps you? A gift from your predecessors, the legends you spoke to?)
I kinda expanded on the idea a bit, but I'd love this as a random encounter event.
Also:
You see a person run by in black and red armor, with an assault rifle, screaming ''ENEMIES ARE EVERYWHERE!''
Why not give us various eye candy about vehicles? I'd love to see the Normandy from Mass Effect do a fly-by over your location in the middle of the desert, and you see like a little box fall off nearby, and inside would be a unique pistol, called a ''Heavy Pistol''.
Also, I'd love to see an AC-130 do a flyby, shooting at some unseen enemy, then just disappearing into the clouds
The USS Enterprise (any version)
(if near the ocean [assuming there is one]) A Covenant ship falls from orbit into the ocean, creating a giant wave. Special item would be washed up (not sure what. maybe a assault rifle or pistol similar to the AR or Magnum from Halo?)
You hear an odd sound in the air, and as you look up, hearing the sound get louder, a passenger jet seems to be crashing down right by you.. it gets lower.. and lower.. and you realize it's about to DIRECTLY HIT YOU! and.. it does right through you (like the ghost images from Point Lookout in Fallout 3).
You hear what sounds like a jet, and you look up, and you see a gold and red man flying by above you (iron man, dur).
..That's all I can think of for now.. but we need more parodies and other funny stuff from games.