Olaf states, "I'm defying gravity." Defying Gravity is a song that Idina Menzel sang in the Broadway musical Wicked.
When Marshmallow is in the ice cave watching the Northern Lights, Luke Skywalker's lightsaber is visibly moving in the snow.
When Kristoff is thrown into the lake and comes out frozen, he is in the exact same pose as Han Solo when he was frozen in carbonite.
An ice sculpture of Mickey Mouse is seen in each different episode!
In season one episode 3, Kristoff builds a shelter for everyone. The rest of the group reject the shelter and say they need to move forward. Kristoff sighs and says "I guess I'll leave this to the birds". The shot then zooms out to show the full shelter. The building resembles the Bates Motel from Alfred Hitchcock's Psycho (1960). The flickering sign on the side resembles Ernie's Bar from Vertigo (1958). Also in reference to Vertigo (1958), the building is topped by a bell tower. The window Kristoff is looking out of resembles the exterior of Jimmy Stewart's apartment in in Rear Window (1954). And of course, the birds that fly in to inhabit the shelter are in reference to the Birds (1963).