The four state capitals not served by the interstate highway system are: Juneau, AK; Dover, DE; Jefferson City, MO; and Pierre, SD.
In this episode, we learn another animal Sheldon does not like; hamsters.
Despite Brent Spiner having become one of Sheldon's mortal enemies in The Russian Rocket Reaction (2011), Sheldon is apparently not averse to dressing up as Spiner's character Data from Star Trek: The Next Generation (1987).
Howard's Borg costume is specifically from Star Trek: The Next Generation (1987). Budget restrictions on Next Generation forced the makers to settle for that particular design. When the Borg re-appeared in Star Trek: First Contact (1996) and Star Trek: Voyager (1995), the bigger budget allowed for a more elaborate re-design. Howard's choice of going for the simpler Next Generation version is probably a way to save money as well.
The comic Stuart presents as a suggestion to the girls, "Fables #1", is a real comic. It's actually called, "Fables Vol. 1: Legends in Exile". The artwork on the cover is the original artwork of the issue. Other reissuings have different artwork, making the original a collectors item.