So far, out of what I have read above, these are the ones I like the best:
Plunger Room and Die Hard reference - both of these vanilla items are perfect for a WW encounter, as mentioned above.
Cafe of Broken Dreams - This should really go in. It's a great reference to earlier Fallout titles, and as mentioned, it gives the opportunity for contact with named NPCs and companions from those games. If this doesn't make it into TTW as a Wild Wasteland event, it is definitely worthy of a mod.
Steamboat Willie - Risewild posted the picture of the mouse. I just wanted to point out that it isn't Mickey, but Mickey's predecessor, Steamboat Willie (1928). The idea is still awesome, though. This one is perfect for a WW reference.
Tin Man - This is another old Fallout reference that I think would be perfect for WW. While I understand that re-using old Fallout encounters may not be for everyone, there are a lot of us who would look at them as easter eggs and who have a feeling of nostalgia for the older games. If we keep it to a few old ones, with some new ones, I think it would be received well.
The Guardian of Forever - Again, this has been referenced in a previous Fallout game, but c'mon...it's probably one of the most iconic things in sci-fi, and it's a cool Star Trek reference that a lot of people would dig.
Time Enough at Last - Wow, this one is an awesome idea. Probably in my top 5 for most memorable Twilight Zones, and it fits a post-apocolyptic enviroment perfectly. Just add a corpse/skeleton with some broken glasses and a note reading "There was time now!!" in the Library of Congress...done. Queue Wild Wasteland sound.
Twilight Sparkles - OMG, this is so funny! Let's face it, no longer are vampires cool like they were in Blade or From Dusk Til Dawn. Now they are angsty sparkly constipated douchebags. Girls will laugh casually, guys will girlfriends will laugh profusely, and guys without girlfriends...well, all they got is gaming, so they'll keep playing anyways.
Evildead - This is pure win. Satanabusjones has a great Dunwich Expansion mod that adds stuff from Evil Dead and H.P Lovecraft, but just dropping a chainsaw and a double-barrel shotgun nearby an "Ash" pile is awesome, and a great WW reference.
Blade Runner - The whole android quest is pretty much based off of Blade Runner, so adding in Rick Deckard works perfectly. Especially since NV includes his gun.
Saving Private Ryan - I also like this one for OA. Great idea!
National Treasure - I like this idea as well, but I would use the name Benjamin Gates instead of Nic Cage, lol.
Men in Black - This one is another great idea for tying in WW to FO3 DLC's, although I am not sure about the neurolizer resetting karma. Just an encounter with the MIB after returning from Zeta would be good enough. (In fact, that is three out of the four DLCs that have a great idea...just need one for the Pitt.)
A Boy and his Dog - Probably some of Don Johnson's finest work, this was a great post-apocolyptic movie from 1975. This one should make it in for sure.
Book of Eli - Again, a great post-apocolyptic movie that deserves a WW reference. Good choice!
OK, here are my few suggestions:
The Road - A man and boy pushing a shopping cart along the road. The man has only a single shot in his gun, and they will wither flee or attack, depending on how the player reacts.
Six-String Samurai - This should really be for NV, but I'm sure we could snatch something from the movie to put in DC. Perhaps the Red Elvises are on tour or the player could encounter a warning about the spinach monster.
Hubris Comics - What comic book location would be complete without a Stan Lee reference? Toss old Smiling Stan's corpse into the Hubris Building with a message scrawled above him on the wall...."Excelsior!" (Be sure to include Stan's signature glasses on the corpse.)
Fear and Loathing in New Vegas - This one again should be in New vegas, unless we can figure out a reason ole Hunter S. Thompson would be covering a story in DC. He could be either a skeleton or a copse, but a drugged out ghoul would be perfect. Be sure to make a reference to bat country, and include a colorful suit and the trademark hat.
The above list is pretty extensive, with at nearly 20 possible encounters. It has something for three of the four DLCs, and it is a mix of vanilla encounters, old Fallout 1 and 2 stuff, and new ideas. I think there is a lot to work with here. If any of these are chosen, I have some additional ideas on how each encounter could work, but I'll save further feedback for now.