UGO: Games within Games

UGO writes,

"These are the best games within games. Not the best old games ported into new games. Nor the best games from mini-game collections. No, these are the bonus time wasters that designers toiled with on the side (or interns were tossed as a bone). These are those Easter eggs nestled in in-game arcades. These are the games that made you forget you were playing a game within another game. "