The following list was posted by ChandlerBing
Get killed or somehow otherwise get to Schottler Medical Center. Enable the "Spawn Sanchez" code. Look at the inside of the hospital from the bottom of the stairs. Keep pressing A on the "Cheat" option of your cell phone until you see a Sanchez appear inside the hospital. Go up to it, and get on the bike. Either all the walls will disappear, all the walls will have inverse colors, or everything will turn very bright white. No matter what, Niko will be invisible and so will your gun if you choose to fire it. The muzzle flash appears but the gun itself does not. You can get on and off the bike. Note: If you try to go outside the hospital, you will become visible again.
Fall through ground
Drive a large vehicle, such as an SUV, to Francis International Airport. Drive sideways under a moving plane so that the wheels are pushing into you. Sometimes you and the car will drop below the world. After a few seconds, you will respawn back on land with the vehicle gone.
Get to the part where you go into the subway about halfway through the mission "Your Shirt, Your Boots, Your Motorcycle". Stay to the left. When the subway car comes towards you, keep left, and try to get in-between the wall and the subway car. Doing this will drop you into "blue hell" for a few seconds before popping you back up.
Go to "Fishmarket South" (where you do one mission for Bernie). Find the Anchor statue near the sea. Go towards the water and over the little dock into the water. Swim to the right (south) until you see a wooden "pier" against the wall. It should have square gaps that you can hop through. Jump through the one to the far right (the first one you swim past), and move towards the wall. You will fall down into "blue hell".
Swim under city
Go to the north part of the map, just northwest of Butterfly Street in Bohan. Then, get down to the outskirts of the land, and walk towards the corner between the brick wall and the cliff. You can walk through the invisible wall. Lookup towards the city to see the city from below. You can also continue onwards and swim under the city.
Lara Croft appearance in Multiplayer mode
Reach rank 1 in all events to unlock all clothes and items. Then, use the following options to create Lara Croft:
Crude humor references
Look at the side of an ice cream van. It reads "Cherry Popper".
Inside the laundromat, the detergent being used and prominently displayed above the back washing machine is "Jizz! Big Washing Power", an obvious attempt at crude humor.
The Brown Note
Near Faustin's house is a reference to a legendary musical note. When you are in the area, proceed to the dead end about a block away towards the water. Hop over the fence on your left while facing the water, and a man should be sitting on a bench reading a book titled "The Brown Note". Musician's joke that this is a note that when played causes bowel movements by the person playing it.
During the intermission sequence for the "I'll Get Her" mission, look closely behind Gerry Mcreary. There is a whiteboard for shift changes for the prison guards. Some of their names are Phil McCrevis (feel my crevice) and Richard Head (dick head).
Reach the part of the game where Niko and Roman have a safehouse in South Bohan. In the house on the left of the table near the television is a pile of books. The middle purple book in a stack of three is titled "Madness & Blasphemy: The Do's and Dont's". This is an reference to the movie 300 where in the "This is Sparta!" scene, the lines "This is blasphemy! This is madness!" are spoken.
Le Fin Absolue Du Monde
This film is referenced in the city and in the in-game internet. Go by Frankfort Ave. in Algonquin to find a poster of a movie called "The Flying Whore". That poster is a reference to Le Fin Absolue Du Monde, the fake deadly-film featured in the short movie Cigarette Burns by John Carpenter in the Masters Of Horror series on TV. To see a funny review of that movie, search for it at the online cultural magazine of Liberty City through the in-game internet.
In Packie's "Three Leaf Clover" mission, while Michael is watching the hostages, one of the men on the floor turns to a man next to him and tells him that he is a member of a gun club and when the time is right they will fight back. When Michael is distracted, the man stands up, shoots Michael, then in turn is killed by Packie and his brother. This is a reference to the bank heist in the movie Point Break.
When shooting at cops, you will sometimes hear them yell "I'm going to be OK!", just like Mr. Orange in Reservoir Dogs. -From: Dom Scarpa
Terminator 2: Judgment Day
The mission "I Need Your Clothes, Your Boots, And Your Motorcycle" is a reference to the line spoken by Arnold Schwarzenegger in Terminator 2: Judgment Day.
The Big Lebowski
While you are bowling, you can hear random conversations in the background. If you listen closely, you can occasionally hear someone order a White Russian, The Dude's favorite drink from the movie The Big Lebowski. The Dude was an avid bowler, and several scenes from the movie take place in a bowling alley.
The Revenger's Tragedy
The final mission, "A Revenger's Tragedy", is a reference to the play and movie based on the play titled The Revenger's Tragedy.
To Live And Die In L.A.
The mission "To Live And Die in Alderney" is a reference to the movie To Live And Die In L.A.
The numbers on blue armored prison transport truck are KSC-303, which is a reference to the main character of the Japanese film Versus, who is known as Prisoner KSC2-303.
Weekend At Bernie's
The mission "Weekend At Florian's" is a reference to the film Weekend At Bernie's.
You can find street art in the style of Banksy, a British street artist, at various locations in the city.
Go to any Cluckin' Bell to find a plastic covering with a man in a chicken suit inside of it. Read the label. It says free "Cluck Norris" toy with every meal.
Sometimes when you walk past a pedestrian they will say "Looks it's your friendly neighbor..., oh no never mind."
In any of the launderettes, you will be able to see an advertisement for the washing powder "FUD", which is a parody of "Daz", which is a laundry powder in England.
Video game references
The "Assassin's Greed" achievement for completing all nine assassin missions is a reference to the game Assassin's Creed. (in Assassin's creed you also had to assassinate 9 people)
Go into any of Niko's safehouses, and watch the television show "I'm Rich". Every so often a blonde girl's story will start, explaining her life. It says what school she went to as a child, which happens to be Bullworth Academy from the Rockstar game Bully.
When Niko hands his CV into the lawyers, it states he attended Bullworth University in England. The Bully game was set in Bullworth Academy in New England.
Grand Theft Auto 3
Across the road from the Bank Of Liberty is a building with some artwork of El Burro, D-Ice and 8-Ball from Grand Theft Auto 3 and the GTA 3 box art, all mixed in with some generic graffiti.
Once you are free to go anywhere, on the first island, go to the map to see an 8-ball logo. When you go there, it is a bar called 8-Ball, an obvious reference to 8-Ball from Grand Theft Auto 3.
Go to Brucie's auto shop. Then, go south down the road. Just before the turn, you can find a wooden Belly-Up fish crate on the sidewalk. Belly-Up Fish was one of the Triad controlled businesses in Grand Theft Auto 3.
In the "Portrait Of A Killer" mission, look opposite of all the gang members you have to kill, at the wall on the big house with three fire stairs on it. You can see an image of a woman holding a gun. She can also be found on the cover art from Grand Theft Auto 3.
On the last island is a destroyed boat and factory. In Grand Theft Auto 3, you destroyed a drug boat for the mob. The boat is at the very top part of the island.
Grand Theft Auto: Liberty City Stories
Some of the ringtones you can choose for the more "modern" phones are actually songs from GTA: Liberty City Stories.
Grand Theft Auto: San Andreas
While watching television in a safehouse, a commercial featuring a NASCAR-like racing event will appear. All of the clips showing the racing are shot from GTA: San Andreas at the airport in Los Santos, using a Hotring Racer.
While watching television in a safehouse, flip through the channels until the "I'm Rich" show is on. After it ends, another episode of it will return, but is not the same episode. Watch through it. At one point you will hear the narrator say "Your life will be as exciting as a soda commercial". At that point, you can see CJ briefly in a multicolored suit freefalling above San Andreas.
Go to a TW@ Internet Cafe, log into a computer, and enter "www.whattheydonotwantyoutoknow.com" as a URL. Go to the thread titled "Health is a gift from space. Worship the Worm". You will see a response from "The Truth", or his online username "Trooth".
Exit your safehouse on Broker, and go to your right down the street. When you get to the intersection, turn right. The second shop is called the "Hot Coffee Shop". This a reference to the "Hot Coffee" mod from Grand Theft Auto: San Andreas.
After your first date with Michelle, try to take it further when dropping her off at home. If you fail, Niko will ask if he can come in for some coffee, and she will reply that he would need $2 million for it, referring to the legal settlement for the "Hot Coffee" incident arising from Grand Theft Auto: San Andreas.
Go on a date with Carmen. She might talk about how she hates living in Bohan and wanted to live in Algonquin. She will then say how Algonquin was too expensive, and says that she would like to live in Los Santos.
Go behind the Memory Lanes bowling alley on Firefly Island, and explore the golf course. Walk around until you see a chicken. It is a miniature version of the giant Feed Seed chicken located in the desert in Las Venturas. You can also find a wind turbine from the game.
When you are in Playboy X's mansion, look under the television to find a blurry Madd Dogg album.
The porno shop found in San Andreas also appears in Liberty City. It is at Star Junction near the corner of Lorimar St. and Denver-Exeter Ave., almost directly in the middle of Algonquin in a very bright area.
There is a bar called the "Vinewood Bar & Grill".
Behind Funland are the Hippo garbage cans from GTA: San Andreas.
On Applewhite St. there is a sign that reads "Visit Las Venturas, $200".
Grand Theft Auto: Vice City
Go behind the Memory Lanes bowling alley on Firefly Island, and explore the golf course. Some of the attractions are actually small models of familiar landmarks from previous games. You can find the Ocean View Hotel from GTA: Vice City.
Across the road from the Bank Of Liberty is a building with some artwork of a motorbike from Grand Theft Auto: Vice City mixed in with some generic graffiti.
The "Pager" ringtone is the same as the Rockstar theme used in the introduction sequence in GTA: Vice City.
When you enter any of the bars, you can see postcards of Vice City.
Red Dead Revolver
Watch the Weazel and CNT channels on the television in a safehouse. You will see a commercial that uses scenes from Red Dead Revolver, which is another Rockstar game.
On Vauxite St. there is a storefront called "Rock Star Music and Video" that alludes to Rockstar Games.