We begin with Super Mario Bros on NES, which contained an interesting fact that many of us might haved missed the first time around. . . .the clouds were the same model as the bushes, just recolored.
Moving on. . . . judging from an in-game screen shot and a picture of the instruction manual, it seems Metroids first made their appearance in Kid Icarus back on the NES.
Mega Man 2 also held a small surprise. In an otherwise tiled background, the big dipper can be seen right before the door to Crash Man.
If you look around Donkey Kong's treehouse in DK64, you see a red girder from the original Donkey Kong, Cranky's phonograph from Donkey Kong Country, and a painting of a dolphin which was the code name given to the Gamecube.
Grand Theft Auto IV seems to have taken its font from an unlikely source.
Here is another way to look at the Half Life logo
Left 4 Dead's logo can literally be seen here in an x-ray during Chapter 2.
Taking a closer look at Super Street Fighter 2 Turbo's cover-art reveals Dhalsim hidden in E. Honda's hundred hand slap.
Teenage Mutant Ninja Turtles II: The Arcade Game reveals that Michaelangelo was a comic book enthusiast, as the Watchman logo can be seen on the bottom of his board. The Watchmen graphic novel was actually released around the same time so this could explain the bridge.
Nintendo likes to throw winks from its first party titles throughout their games. In The Legend of Zelda: Ocarina of time, after meeting Princess Zelda for the first time as Child Link, a peek into a nearby window at different angles reveals three very interesting portraits decorating the wall of Hyrule Castle - say hello to Super Mario, Bowser and Luigi.
On a same note, in Legend of Zelda: Majora's Mask, taking a closer look at the masks might have helped us to see this connection. . . .
To the Left, we have the level "Silent Cartagropher"from Halo 1, and to the right, the last level in Halo 3 titled "Halo".
Pokemon and its many sequels all take place in actual Japanese provinces.
On the same note, World of Warcraft might have taken a page from pokemon's book. . .
And last but not least. Glados from Portal was seen as the enemy, the antagonist, who broke free from human clutches and went berserk in the facility. A closer look could reveal otherwise....
And there you have it, some great video game facts from the Neogaf boards. Definately worth a look as I left out many, many other tidbits. You can find the link to the forum here http://www.neogaf.com/forum/showthread.php?t=232550
-Frank