An eagle neighbor whose name is Pierce... and whose Verbal Tic is "hawkeye.". There's also a frog named Jeremiah (whose portrait in Wild World states that he is, in fact, a bullfrog, with it pointing out that "blue frog" and "bullfrog" sound similar, due to his blue color).
In City Folk, Kapp'n's trophy from Super Smash Bros. Brawl can be seen near Kapp'n himself while riding on the bus.
Goldie's picture quote in Wild World onwards: "I'm really into that Lab on the cover of Nintendogs. He's pretty dreamy." To be specific, she's referring to the labrador retriever on the box art of Nintendogs: Labrador & Friends.
The Creepy Clock furniture item is almost identical to the "13-hour clock" from The Haunted Mansion.