There's a shop in the mall called "Jerk Store". (Three of them, if you look closely. Must be a chain.)
And another one called "Floor Mart".
And another called "Ugly Baby".
Confrontation, a political debate show in the vein of Crossfire and Hardball.
Ilana's clothes at the end of Episode 4 look a lot like Velma Dinkley's usual outfit.
The first fight scene. The army's firepower does nothing to the monster, and then its first attack knocks the Titan flat on its arse against a building. Shades of Shinji's first fight in Neon Genesis Evangelion.
When Xishi Mind Rapes someone, their bodies become more vascular, much like what happened to Ayanami Rei.
Episode 8 bares a number of similarities to Harry Potter. Orphaned youth with chip on his shoulders; check. Blonde-haired perfectionist with two hench-friends who antagonize the boy; check.
Baron's aristocratic name, long nose, and hairstyle marks him as a younger counterpart to Osamu Tezuka's character Duke Red.
Episode 8 also had short plump young boy with red hair and big eyeglasses. Hmmm...
The farm in "Tashy 497" is the exact same one from Courage the Cowardly Dog. All that was missing was an old lady yelling at her grumpy husband because of the house blowing up and the man blaming it on a pink poodle.
Eerily, the farm house and it's surroundings seem to be completely abandoned and decaying.
The Titan resembles a semitransparent version of Gigantor.
Galaluna and the Mutraddi beasts recalls similar concepts from Voltron. As does Lance and the Princess.
The organization designed to protect Earth from alien invasion is called GGG.
G3's standard soldiers' outfits look a lot like those worn by Red Impulse, although the helmets are reminiscent of Bioman's.
On the subject of Gatchaman, Lance can be considered an expy of Joe Asakura, and his father is a dead ringer for Dr. Nambu.
Right before he stretches out his nose, Octus' shifting disguise in episode 11 looks suspiciously like Nick Cave.
Those G3 bipedal mechs that appeared near the end of episode 11 bear a striking resemblance to Zentraedi battlepods.
Scary Mary's last name is Cavanaugh, a reference to Christine Cavanaugh, the original voice of Dexter, who retired from voice-acting in the early 2000s and became very reclusive ever since. Scary Mary's appearance seems a visual shout out to Velma Dinkley.
Her first name might also be a reference to Mary Kay Bergman, a voice actress who passed away in 1999, and played Daphne Blake for a while.
Newton holding the boombox over his head was obviously inspired by the romantic gesture from Say Anything, although he seems to be Comically Missing the Point, given that he's playing commercials instead of a love song.
In the episode "A New Beginning", General Steel drives what he calls "THE HAMMER!" and proceeds to beat up a monster while saying "Can't touch this".
In "The Demon Within", Ilana mentions that the only one of her arranged dates on Galaluna she was actually interested in was "Prince Simon of Duran," a reference to Simon LeBon.
During the series finale, after the HMER gets wrecked, Steel blasts away at the enemy with an assault rifle in a manner very reminiscent of Dozle Zabi in Mobile Suit Gundam. He's lucky enough to not meet quite the same fate, though.
The monster in "Roar of the White Dragon" looks an awful lot like Clover from Cloverfield.