Unfortunately I don't have screenshots, but in Mass Effect 2 you can buy a "Space Hamster" as a pet from Citadel Souvenirs, and it squeaks, too.
One of my favourite Easter Eggs that made me smile when I discovered it was in Siege of Dragonspear.
If you use the Spectacles of Spectacle in the Coalition Camp in chapter 10, you can draw the genie Nazramu into the Prime Material Plane. He sells some unique items, supposedly gathered during his travels across the planes.
On of those items is a "wizzard hat" that gives +1 casting speed and +2 movement speed, because "A wizard who runs away from combat lives to run away another day, after all."
That's a reference to Terry Pratchett. Rincewind, the main character of his first books, is a wizard who is famous for running away really often and fast, and he wears a hat with the misspelled word "WIZZARD" written on it.
Sir Terry Pratchett, you are deeply missed.