Keep clicking the eye icon on the trees, because you'll eventually get one called a "Daventree". This is a reference to Daventry, the main setting of King's Quest.
Every now and then when the Gargoyle above Erasmus's house asks "What is your Quest?" (obvious Monty Python joke) one of the answer choices is "I want to be a pirate!" This is, of course, a reference to The Secret of Monkey Island. If you select it, the Gargoyle says "Boy, have you got the wrong game," and sends you back down the mountain.
When the gargoyle above Erasmus's house asks the name of the hero, one of the answer options is "Call me Ishmael." This is a reference to Moby Dick.
The most common password to the thieves guild in the game is 'schwertfisch'. Schwertfisch is German for swordfish, which in turn is the password to a speakeasy in the Marx Brothers movie Horse Feathers.
The town of Spielburg is, of course, named after Steven Spielberg. Sam the beggar also makes a reference to Amblin, which is Steven Spielberg's production company.