Assassin's Creed
The "Assassin's Greed" achievement for completing all nine assassin missions is a reference to the game Assassin's Creed.

Bully
Jimmy from Bully can be found walking outside the Hove Beach railway station at certain times.

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.

At the end of the opening sequence for Elizabeth's second mission, you can see Jimmy Hopkins, the protagonist from the game Bully, dancing in the back.

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.

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 first mission, when you give Roman a ride to a betting shop, on the other side of the road is a shop called "Mr. Wong's", which is reference to Mr. Wong in Grand Theft Auto 3. Also, there are Furgons in the city.

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.

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.

Salvatore's run-down mansion can be found in Alderney, near Beaverhead Ave. and Cassiar Ave.

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
After you have access to the Bohan apartment, look on the floor next to the table using a sniper rifle. You will see some albums, one of which is by Og Loc. Og Loc was a character from GTA: 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.

Behind Funland are the Hippo garbage cans from GTA: San Andreas.

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.

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.

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 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".

In Algonquin near Star Junction is a billboard with "Prolaps" on it. Prolaps was a clothing shop in GTA: San Andreas.

On Applewhite St. there is a sign that reads "Visit Las Venturas, $200".

The "www.freejames.org" and "www.area53site.com" websites allude to James Pedeaston and Marvin Trill, DJs on WCTR in Grand Theft Auto: San Andreas. James has been arrested and has a charity set up for his legal funds (with only $23 in it), and Marvin Trill has shut down his show to protect his research.

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".

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.

Watch the Weazel and CNT channels on the television at your hideout. You will see various locations from San Andreas.

When you are in Playboy X's mansion, look under the television to find a blurry Madd Dogg album.

Grand Theft Auto: 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.

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.

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.

Grand Theft Auto series
After you kill the drug dealers in the "Shadow" mission for Little Jacob, leave the room, and go back the way you came. On the wall just before you go down the stairs, you will see graffiti which has the name of every previous Grand Theft Auto protagonist on the wall; Claude from Grand Theft Auto 3, Tommy from Grand Theft Auto: Vice City, Carl from Grand Theft Auto: San Andreas, Tony Cipriani from Grand Theft Auto: Liberty City Stories, and Victor Vance from Grand Theft Auto: Vice City Stories. The text says things like "Victor - never forget you / always remember you bro", "RIP Claude", "RIP Toni", "remember Tommy - u r still my hero", "Carl I love you RIP everyone miss you", "RIP Vic".

Got to the museum in Algonquin. In front of the museum you will find drawings of characters from previous Grand Theft Auto series games.

Halo
While watching television in a safehouse, flip through the channels until you find the cartoon show called "Republican Space Rangers". The design of their spacesuits resemble Master Chief's suit from Halo.

Non-Uniform Rational B-Splines
There is "NURB RENDA" graffiti in Dwayne's building. This is a reference to the NURB rendering that has replaced standard polygons and is commonly used in newer video games. NURBS (or Non-Uniform Rational B-Splines) are mathematical representations of 3-D geometry that can accurately describe any shape.

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.

Rockstar Games
On Vauxite St. there is a storefront called "Rock Star Music and Video" that alludes to Rockstar Games.

World Of Warcraft
Go to a TW@ Internet Cafe, log into a computer, and enter "www.myonlineme.com" or "www.myonlineme.net" as a URL to see a parody of World Of Warcraft. "myonlineme" is shortened to MOM which is WOW (World Of Warcraft) upside down.