Dave's shirt on the cover of the Maniac Mansion box declare's his love for LucasFilm Games.
In the enhanced version of Maniac Mansion, there is a poster on the left wall of the game room. If you look carefully, it is a poster for Zak McKracken and the Alien Mindbenders. And, in Zak McKracken and the Alien Mind Benders, in the pawn shop, there is a poster for Maniac Mansion. Great cross-promotional advertising.
In the original game, the license plate on the Edsel in the garage reads "THX 1138", the title of a George Lucas film. The number 1138 is also a possible number for the meteor police. In addition, if you look at the large speaker in Green Tentacle's room, you'll see a reference to "THX Sound".
In Green Tentacle's room is a large tour poster. Read or Look at the poster, and it reads "See Rob Gilbert Live at the Forum." Ron Gilbert is one of the head creators of Maniac Mansion, as well as the lead designer of the SCUMM engine.
In the NES version (only), there is a record on the table. If the player reads the record, they will see that it says "Loom Sountrack Album." Loom is a LucasArts graphic adventure that was released in 1990, the same year as the NES port of Maniac Mansion. Also, if you play the record on the Victrola, it plays the first two seconds of the Glass City theme from Loom. This record has no purpose in the game. The other record, that is in Green Tentacle's room, is one that is useful.
In Weird Ed's room is a purple pennant. If you read it in the PC version, it reads "L. F. L. U. Rah!" LFL is the legal abbreviation for Lucasfilm Ltd.
In the NES version, the pennant is invisible, but still exists. If you read the invisible pennant in the NES version it says "SCUMM U. RAH!". SCUMM is an acronym for the game engine that was created for Maniac Mansion, and SCUMM U was the LucasArts training program for SCUMM developers. The NES port of the game was modified to make the game more suitable for younger audiences. One of the modifications, requested by Nintendo, was to remove any reference of "SCUMM" (perhaps because the word was consider profanity). This is probably why the pennant was "hidden", but not removed by the tricky developers.
Also, note the x-wing fighter toy on the cieling.
In Maniac Mansion, one can find a painting in the dining room and a statue in the hallway (Note: in the NES port of the game, the statue and the painting were removed for censorship). In the LucasArts graphic adventure game Indiana Jones and the Last Crusade, these same works of art can be found by Indy in the art room of the Nazi Brunwald Castle. The writing on the statue's plaque is also identical in the two games.
In the kitchen is a chainsaw. If you try to use it, you'll find out that'is out of gas and you're not able to use it in the game. Alternatively, in the LucasArts adventure game Zak McKracken and the Alien Mindbenders, there is a can of gas. Perhaps the programmers mistakenly placed the gas can in the wrong game ... or purposely added this nice little tie-in.
In the mansions library is an unusable plant called "Chuck the Plant." Chuck has made an appearance in several other LucasArts games, including Indiana Jones in the Last Crusade at Henry's house, and in Maniac Mansion's hit sequel Day of the Tentacle in the mansion's lobby.
In the NES version, when one of the kids or Dr. Fred plays the Meteor Mess arcade game, you may notice that the first five notes of the Mario Bros. theme song is played.
After fixing the radio in Fred's bedroom with the radio tube, the radio can be turned on. When a kid calls the Meteor Police in the NES version, the first four notes of the Indiana Jones theme song is played.