In the DLC world Roaring Heights, the School building seems to spell "SCHOOL OF COCKSUKRS" mirrored and upside-down.
In the Into the Future expansion, there is a pre-made house called "Formerly the Plains Express household" with the members Fryderyk Rama, Lilah Turni and a Plumbot named Bend0. This is a reference to the show Futurama, specifically Planet Express, Fry, Leela, and Bender.
If a Sim with the Investigator profession is on a stake-out, there is a chance that this Sim will reference the case of Bella Goth. Bella Goth first appeared as a playable character in the console version of The Sims. Later, in the Sims 2, she appears to be missing from her family's neighborhood, Pleasentview, and found with no memories in another neighborhood, Strangetown. This reference seems to be a plot-hole, however, as Bella appears as a child in The Sims 3; which is supposed to take place 50 years before the events of The Sims.
There is a reference to the Mass Effect series in the ambitions expansion. When using the time machine to travel to the future, your Sim appears in a crowd of people cheering about how a shepherd saved the galaxy from a 'huge ancient machine God threat.' Additionally, the futuristic outfits that can be obtained from the future highly resemble the Spectre armor found in Mass Effect.