Tomo idolizes Fujiko Mine of Lupin III, which is why she lets her hair grow during the second year; the anime even adds an Imagine Spot of Tomo as a Fujiko expy. Of course, she forgets to consider changing the hair style as well, so she decides to go for looking like Ryoko Hirosue instead (Ayumi Hamasaki in the anime).
Chiyo-chichi's infamous "I wish I were a bird!" comes from a commercial for the Nova chain of English-teaching schools.
The way Yukari downs a glass of liquor (plus the accompanying Beergasm) is more than reminiscent of Misato Katsuragi's famed shtick. Kiyohiko Azuma was previously well-known for his Neon Genesis Evangelion doujins and based Yukari off of his take on Misato, so the reference is more than appropriate.
Kimura's (rejected) sketch for Chiyo's cheerleading costume in episode 15 is basically the same as Pretty Sammy's; it's also a shout-out to Azumanga author Kiyohiko Azuma's Pretty Sammy parody doujinshi work.
Late in the manga's run, Tomo compares Yomi's singing voice to Gian from Doraemon (a well-known Hollywood Tone-Deaf anime character). The ADV translation has her compare Yomi to King Louie, while the Yen Press translation changes it to Homer Simpson.
In the costume couple race in the third year's Sports Festival, Chihiro dresses as the Spirited Away character of the same name, partnered with a classmate dressed as No-Face from the same film. Due to rights issues, the reference is omitted in the anime (despite Studio Ghibli doing background art for it).
The way Chiyo's dad says "I am a cat" ("Wagahai wa neko de aru") is a reference to the book of the same name, which features the protagonist speaking in similarly overblown and uncommon grammar reserved for nobility. Then again, he might just like overblown grammar.
Exclusive to the ADV print of the manga: after a customer purchases food from Magnetron Burger with Chiyo at the counter, he turns around and asks if he's onCandid Camera. Other translations keep the same idea, but don't specifically mention Candid Camera.
