King's Quest I has several Easter eggs hidden in the game. All of these Easter eggs found courtesy of Erpy walkthrough.
Look at the smoke rising from the cauldron several times. On occasion, a face of a monster appears.
Note from witch's house
If you read the note from the witch's house several times, every once in a while it will read something else.
More to come
(More to come, I just don't feel like rewriting what Erpy has already written!).