Hell, Gay Deceiver and her magic bathrooms count.
Santa’s bag of toys.
Pee Wee Herman’s bike’s saddle bag.
Pig-Pen’s shoes.
That’s because it exists in L-Space. And Hex has been mentioned; its drawers are not only capable of expanding in three dimensions, but in every dimension. Not mentioned are Gallifreyan paintings, which can contain at least an entire living city.
Also, the Gay Deceiver, the car in Heinlein’s novel The Number of the Beast. After the four main characters visited the Land of Oz, the car acquired a full bathroom.
Also, remember Land of the Lost, the weird 1970s children’s show? There were these pylons that appeared on the outside to be roughly the size of a phone booth but were much bigger inside. And they had these tables on which various stones could be moved to alter the climate and other things.
Oh, and the Luggage.
One writer opined that the kibisis, the magical bag that Perseus carried (and into which he put the Gorgon’s head) magically got bigger inside to accommodate whatever he put into it, and used this claim to bolster his pet theory about the origin of the myth. The thing is, I can’t find any reference at all to the kibisis doing such a thing, in either ancient or even modern sources.
The Harry Potter universe has been noted, but in particular we see in the movie that the tents they set up the World Cup in Harry Potter and the Goblet of Fire are much bigger inside than out.
The green limo of the Leanansidhe at the end of “Changes” in the Dresden Files books
The hat in the intro of “Liddsville”
The wardrobe in the Chronicles of Narnia (really amazed nobody got that one yet!)
They did. Someone mentioned “Professor Kirke’s wardrobe” a while back.
Ah, missed that! I should have searched for “wardrobe” instead of “Narnia” on the page. 
The submachine gun magazine in just about any movie with a submachine gun.
Clark Kent’s suits, especially in the older comics. No way does Clark have the same huge shoulders and chest as Superman. His suits have to be bigger on the inside than on the outside.
There was a song from the '50s called “She can’t find her keys”, about a guy who’s waiting for his goodnight kiss after a date, but his date can’t find her keys among all the other thins she has in her purse. She eventually pulls out such improbabilities as an army cot, a watermelon, and a fire hydrant, but still no keys.
The Narnian wardrobe has already been mentioned, but we should also acknowledge the stable in “The Last Battle” which had a whole world in it. And, in that world was a garden, which had another, bigger world contained within it.
Is Inspector Gadget an object?
It may be worth mentioning the related phenomenon of hammerspace. It has been suggested that some of these objects appear to have infinite capacity because they offer access to hammerspace.
Yes: a world inside a garden, in a world inside a stable, in a world inside a wardrobe. Not many examples can beat that :).