GTO: Great Teacher Onizuka (TV)

Onizuka's favorite actress in the anime is Nanako Matsushima, who plays his love interest in the live-action drama version. Coincidentally, Matsushima is married to Takashi Sorimachi, who played Onizuka in that series.

In the episode 8, when Murai stepped on a fermented soybean and got mad at Onizuka,as his face was zoomed in, you can see a mark in his forehead the word "kill" in kanji.. 

Starting around episode 28, Onizuka sometimes wears a T-shirt with the famous "Tongue and Lips Design" logo of the Rolling Stones.

In Chapter 3, onizuka make a direct parody of Kenshiro, but the star sign in his chest is backwards 

In chapter 10, in 11:20 Onizuka arrives with a motociclist named "Kenji", his name and his mustache are the same as Harima Kenji from School Rumble 

The brand of cigarettes Onizuka smokes is Mild Seven (now known as Mevius), an actual brand of cigarettes exclusively sold in Japan.

In episode 1 when Nanako is cooking for Onizuka and he is in the background getting dressed up as a wolf and setting out the bed roll, there is a song playing in the background (presumably on the radio). The song is famous in Japan and talks about how boys are wolves that just want one thing from girls, so the girls should beware.

In Episode 12, when Onizuka gives Fuyutsuki a ride on his motorcycle he is wearing a Met helmet from the Rockman (Mega Man in the USA) series of video games.

In episode 12 the character Suguru Teshigawara parodys Gendo Ikari by wearing white gloves and a black suit to go along with his glasses in his dream sequences. He even does the "close shot of head angled down and slightly offset with three fingers pushing his glasses back up his nose while the lenses reflect the light thus rendering them opaque" pose.

The plot in episode 22 marks the first episode in which the entire plot was not be based on a pre-existing GTO manga chapter.

In episode 23, when part of Murai's gang is searching for Onizuka in the movie theater, the movie playing in the background is the famous TV scene in the movie, "The Ringu."

In episode 25 - legendary street racing queen "Hakosuka" drove Nissan Skyline GT-R coupe (KPGC10) released in 1971.

In episode 31, the slot machine that Onizuka cheats with a magnet is "Lupin IV" themed. Coincidentally, Tony Oliver plays both Lupin III (in several incarnations) and Murai.