This isn't technically an easter egg, but it's part of an egg, and it made me feel warm and fuzzy and reminded me of my childhood. So when you find the suffer, you can look at it in your inventory and it laughs. That laughter is the exact same as this weird little laughing fuzzy monster toy my parents had when I was young. You'd shake it, and this long stream of laughter would start, ending with the laughter you hear the suffer emitting.
Like I said, not really an easter egg, but that laughter was taken from something that led to a lot of nostalgia for me. I wonder where that toy is now? Probably packed away in a basement somewhere...