Back With a Vengeance - S2-E13
Trivia: About all of the aliens found in attendance of Kevin's mega cruiser strangely resemble those individuals previously seen (on the selfsame ship) in episode 2-5, "Grudge Match", whereas they should have escaped the cruiser near the end of that episode.
Weiner of Our Discontent - S4-E18
Trivia: Roger has various weird objects stored up in the attic some used as furniture for his own means. One which contains the address to Roger's spaceship, which is hidden away in storage as shown in this episode.
The Library - S2-E10
Trivia: Wan Shi Tong is of one the few things in this show that is not a reference to Asian cultures, but to Ancient Greece instead. In their mythology owls were the symbol of wisdom and their goddess of wisdom, Athena, was often depicted with an owl.