Adam's design is similar to Molly Millions from Neuromancer
In Pritchard's office, you'll find two old, red PC expansion cards on a wall in display cases. Close inspection reveals that they are Gravis Ultrasound cards, with the top card being the Ultrasound Classic while the bottom one is an Ultrasound PnP Pro. The top card's lower-right corner also has a close-up shot of an IC highly resembling the original Ultrasound cards' GF1 chip, but with edited text.
One of the prostitutes in Detroit is named Charlotte, confirmed by the Director's Cut commentary to be a direct shout out to the Iron Maiden song "Charlotte the Harlot".
In the police station, you can overhear two cops discussing some 80s movie set in Detroit that had a robotic police officer. One of the two is even named Alexander Murphy, and one of the e-mails on his computer mentions an Officer Lewis. Given the very similar Detroit-cop-gets-beaten-to-death-and-rebuilt-with-technology, this is a pretty deliberate Lampshade Hanging.
There's another Robocop shout-out on a computer in the Detroit LIMB clinic, which references Jensen's augmentations; specifically that his left arm and legs were salvageable but were replaced at Sarif's request. A similar scene occurs in the first film, where Murphy's left arm is initially saved but then replaced to fit OCP's plan of "total body prosthesis."
Jensen punching through walls to get to people is also taken directly from Robocop.
Not to mention the security log-in for mpost, whose first name is presumably Mike, and whose password is blues
If the Detroit cops have a sci-fi theme, the Picus employees have a sports theme. There is a P. Kane, a Seguin, and a Messier.
You can find an email in which someone says they should go to a Spos game and they're going to win because Strasbourg is pitching that night. Looks like by 2027, Montreal took the Expos back from Washington. They also mention he's retiring that year, which would be a long but not unimaginable career for Nationals pitcher Stephen Strasburg..
One of the sportswriters is named Red Fisherman, after Montreal sportswriter Red Fisher. He mentions he's starting a column following the Enhanced Hockey League — Red Fisher covered the Habs for years.
You can also find some hate mail written to the sportswriter referring to "the worst move this team has made sice they gave up on Carey in 2012." I guess we can expect a lousy season from Carey Price.
There's a pocket secretary that lists all of one guy's passwords, including his fantasy hockey password, which is "leafssuck67." They still haven't won the Stanley Cup by then?
Passwords in the Sarif building include "tigers" and "redwings" (respectively, Detroit's professional baseball and hockey teams), and David Sarif himself is never seen without a Tigers game or scouting report on at least one open terminal. Someone at Eidos is a sports fan.
Additionally, before you rescue him, you can spy on his cell from above while travelling through air ducts, like you could do in MGS with the DARPA Chief and Meryl.
There is a sidequest-important character in Hengsha named Lee Hong, who shares a name with a character from another Eidos game series.
The manner in which you can stage Diamond Chan's suicide during the "Rotten Business" sidequest, and the picture for the Achievement/Trophy you unlock for doing so, are also reminiscent of this same franchise.
One of the eBooks the player can find mentions a listing of media stream subscriptions, and the news feed mentions an interview with "elder rocker JoCo."
On your first visit to Hengsha, near the end, there's a computer in one of the rooms near Zhao's penthouse that contains an email directed at a "Kevin Mitnick."
Several e-mails found on various computers in Singapore are almost directly paraphrased from the automated speech of the Black Mesa Transit System.
If you let Zeke live in the Milwaukee Junction level, you get an achievement called "Unforeseen Consequences." Those have become Arc Words in the Half-Life series.
Highway overpass in Derelict Row is marked HWY 17, a level name from Half-Life 2.
Emails found in the Picus Sub-Basement involve one employee complaining that the statue of the MJ-12 logo looks like it belongs in a Bond movie.
In the Omega Ranch complex, there is a computer with an email from 'Dwayne' addressed to the security staff, saying (in unnecessarily fancy language) that he wanted to requisition a camera to try and catch who was repeatedly putting animal porn on his computer, suspecting that it's one of his fellow scientists. It's revealed on another computer that three guards, 'Mark,' 'Lou,' and 'Abigail,' are behind it, and are tempted to humor Dwayne by giving him a camera and repeating the process while wearing an office lab coat. It becomes clear what the Shout-Out is toward when Mark mentions, "I can't wait to see the look on his face when he sees what I did with his stapler."
And later, when you find Dwayne's computer, not only does it have conspiracy theories in the outbox, but the general message he sent out includes a postscript accusing someone named 'Jim' of stealing his stapler. It doesn't get much clearer than that.
Elsewhere in the Omega Ranch, a security memo to all staff from the admin team is a "Urinalysis and Radiation Screening Reminder", and is a word-for-word quote from the original Black Mesa Commute. Later, there's also a "Safety Policy and Regulation Reminder", an "Annual Interdepartmental Mensa Competition Reminder"...
During the quest with Brent Radford, if you listen into the conversation between him and his attacker, he will ask if he is getting a new rug, since it really tied the room together.
In the Detroit police station the hacker's body has been classified Ultraviolet and is off-limits to Blue clearance. One of the classic era supplements was HilSector Blues in which the Alpha Complex police were all classified as Blue security clearance.
Praxis points and kits are very similar to cyber-modules in System Shock 2.
While we're at it, the 10mm Handgun looks very much like the one from SS2
And even larger one comes when you look at the boss fight with Fedorova. Circular room with a large AI core in the center? A woman running around the perimeter doing her best to kill you? Various consoles that can make your life easier? Sounds a lot like the final boss fight with SHODAN, if you ask me.
You can discover an email from one "veronica_m" who's working in the sleuthing business.
There is a GURPS SWAT RPG sourcebook sitting on one of the desks in the police station.
In the "Acquaintances Forgotten" mission, you can read a note on one of the MIBs that details "Mr Grey"'s iteniary. It includes stopping at a place called Wimbledon Bridge House. This building exists in Real Life and is one of Square Enix's registered offices.
There's a sniper rifle on the roof of a gas station. It's entirely possible to get it during the 2nd chapter, even though the normal method for obtaining it requires you to hack a level 4 security panel. Hint: There's a barrel outside of the gas station, and a vent on the inside positioned just above a rack. You can use the barrel to jump up and grab it before you fall.
You can also just use a barrel or the high jump augmentation to climb the red dumpster behind the gas station, from which its trivially easy to jump up to the roof.
The Plasma Rifle shares a lot of characteristics with the Quake 3 BFG10K. Both are extremely rare, state of the art weapons. Both shoot powerful green projectiles that cause splash damage. When the characters hold them, only small portions of the tips (of otherwise pretty massive guns) are being shown. To top it off, the rate of fire is nearly identical. The plasma rifle's description even seems to be a shout out, as it states targets can occasionally be vaporized by the gun. This doesn't actually happen in the game, but was really common with Quake 3's BFG.
Over the road from the Detroit Police Station is a building that resembles the Million Dollar Theater in Los Angeles. This is presumably another shout out to Blade Runner, as the real world building is shown in several shots because of it's location across from the Bradbury Building. The game version is even called "MDM," which is obviously meant to be Million Dollar Movies or similar.
In one of the more obscure references to this film, the construction site that Malik crash lands in when returning to Hengsha is run by a construction company called Shimata-Dominguez. In the 1992 director's cut of Blade Runner, the tail end of the blimp advertisement states that this is the company responsible for building the off-world colonies.
One of the computers in Tai Young Medical belongs to a Ms. Tam. This may be coincidental, as Tam is a (relatively) common surname in China.
When the Japanese dub of Human Revolution was announced, people were not surprised to see Atsuko Tanaka voice the Big Bad of the series...given how she was most famous for her role as one of Cyberpunk's most famous works.
The occupant's name is listed as "JaneDoe1964-7", the years Gilligan's Island was initially aired.
Coordinates given for the island on which she was found match those given by The Professor in the episode, "Big Man on a Little Stick".
An email exchange between a base officer and a logistics officer has the logistics officer advising the base officer that if he is really serious about getting a pizza oven, he should just fill out one of the standard machine gun requisition forms, cross out the machinegun model, and write "pizza". This is something a requisition officer once told the doctors of the 4077th that they could do, after telling them that they could not get supplies they actually needed.