There's nothing that gives me more pleasure than unexpectedly spotting Godzilla or his friends in a movie that isn't about him. Here is a list of flicks where i've spotted Godzilla figures, models, posters, etc.
Serial Mom - Beverly's horror movie buff son Chip had a Godzilla model in his room on a shelf. You can spot it behind Kathleen Turner's head when she asks to watch the tongue mutilation scene in Blood Feast.
All Over The Guy - Gay romantic comedy. One of the guys is into collecting Planet of the Apes figures, and at one point they go to a comic shop where there's a shelf in the background with a few Godzilla figures. I instantly spotted Bandai's Godzilla 2001 with the glow fins.
Creepshow - The intro at the beginning where the kid gets scolded for reading "trash", aka horror comic books. He has a Mattell Rodan hanging from his ceiling.
Mars Attacks - There's a brief clip of Godzilla smashing through a building (I think it's from Godzilla vs. Biollante) while the aliens are flipping through television channels.
The Deadly Spawn - Awesome 80's horror flick about alien creatures hiding out in a family's basement, there's a kid in it who is into monsters and has a Mattell Godzilla in his room.
Friday the 13th Part 3 - After the male half of token sex couple gets hacked in two, his girlfriend is laying on a hammock reading Fangoria magazine. She flips to a page that has an article on the 25th anniversary of Godzilla. One page has a reproduction of the American poster for Godzilla vs. Megalon. Blood drips on the magazine and she looks up in time to see her dead boyfriend before Jason slams a knife through her chest.
Pee Wee's Big Adventure - During the bike chase scene at the end, Pee Wee goes through several movie studio lots, one of them happens to be during the filming of a Godzilla film, with an actor dressed in a rubber Godzilla suit fighting a dangling paper maché King Ghidorah.
Antibodies - German thriller about a small town cop who interrogates a serial killer to get answers regarding an unsolved murder. There's a scene during a kid's party when the camera sweeps across a table, where an Imperial Godzilla figure is sitting on. That was the big highlight moment of the film for me, as the ending to an otherwise decent story was a big letdown.
O Fantasma - Foreign flick about a young trash collector named Sergio who seems to live in his own fantasy world. While on his trash collecting route he runs into a handsome young man and quickly becomes fixated on him. He eventually breaks into the guy's house and, while spying through his bedroom in the dark with the light from his lighter, you can see a Godzilla figure on the table next to a computer. Then in the next scene he pees all over the guys bed while holding the Godzilla figure in his hand.