Sorry if this weird scene has been mentioned 4,767,234 times before, but I got to point it out, 'cause it's really cool.
In "Put Your Head on my Shoulder", otherwise known as "the one where Fry's head is put on Amy's body", the is a monolith floating in space with an "Out of Order" sign taped on it! The screen passes by it just as Fry and Amy are on their way to Europa, one of Jupiter's moons. That's roughly where Dave Bowman and HAL encountered the monolith in 2001: A Space Oddesey!
As for the "Out of Order", it may be an obsure reference to the fact that by the end of Arthur C. Clarke's novel 3001: The Final Oddesey, all of the monoliths have stopped comunicating. Or it could just be a silly Out of Order sign.