High School of the Dead (TV)

A few of those credited as "Them" are staff members on the anime, including animation director/character designer Masayoshi Tanaka, ED singer Maon Kurosaki, and the source manga's artist, Shoji Sato.

There is a OVA.

in episode 1 at the observatory when hasashi died and when the sun started to shine the song that being played is the same theme song of the 28 Weeks Later Theme/Don Abandons Alice by john murphy

In episode 2, the character Kouta Hirano is introduced. He bears a striking resemblance to the real Kouta Hirano who created the Hellsing anime

In episode 3, the name of the convenience store is "Sevenson", a cross between 7 Eleven and Lawson. Furthermore, the cashier resembles Shaun of Shaun of the Dead.

In episode 4 the name of the self-service gas station is "Shaun" the same name as the protagonist in the "Shaun of the dead" movie.

In episode 4, the self-service gas station "Shaun" is also a parody on "Shell" gas stations.

In episode 5 around 6:23 you can see a poster that resembles Naruto, and other posters too.

In Episode 5, Hirano makes a point of exclaiming his double tap when killing a zombie, possibly a reference to to the movie "Zombieland".

In episode 5, Bae Yong-joon, a Korean drama star, was shown as a zombie.

In episode 6, the scene where the little kid bit the mother's neck may have been a reference to "Quarantine", a movie where a very similar scene occurred. 

In Episode 6, Kouta Hirano says "I like turtles" after seeing Saeko virtually naked. This is reference to a highly viewed video and meme where a kid who is dressed as a Zombie says "I like turtles."

In episode 8, Hirano references "The Rat Patrol" at about 8:30 in.