I'm not sure if this is a game or not, but heres the deal. I'll start by naming one easter egg within a game and then the next person does the same thing. Okay, here goes. When Playing Osu! Tatakae Ouendan! or its sequel, side to side with Elite Beat Agents, you'll notice that although the Ouendan Squad and the Agents have the same exact occupation, their moves vary greatly. The Agents moves are a lot fruitier and more exaggerated, while the Ouendan Squad's are just plain old cheering moves. What's up with that?
In Call of Duty 4: Modern Warfare, when play online or in a custom game on the map Backlot, on the red bow thing in the middle of the map, the number on it is 1337, and we all know what that means. XD
In Dementium : The Ward. Theres a hallway that has documents on the walls. One of them says a patient's disease was "Video Game Thumb"
The Legend of Zelda:Ocarina of Time When you meet Zelda for the first time in the garden,take a look at the right window.You can see a portrait of mario,luigi and yoshi!XD
When you play Metal Gear Solid on the PS1, in the room where you fight Gray Wolf, you see a frog figurine that you can shoot. But in The Twin Snakes on the GameCube, that same Frog Figurine are replaced by Yoshi and Mario. Throwback to Nintendo taking in Metal Gear.