Muteki Choujin Zambot 3

There once existed a planet named Beal, until it was wiped out by the mysterious entity known as Gaizok. The few remaining survivors escaped to Earth and split into three families, named Jin, Kamie, and Kamikita respectively. While attempting to start a new life, the collectively known "Jin Family" prepared for the inevitable Gaizok invasion on Earth and its giant mechanical beasts known as "Mecha Boosts". In order to defend their new home, they have built three vehicles which when combined form the mighty Zambot 3. The Jin Family must not only defend against Gaizok attacks, but also harsh criticisms from the very people they protect, who blame the Jin Family for the invasion in the first place. (Source: AniDB)

God Mars

In the year 1999, humanity begins to advance beyond the solar system. The leader of the planet Gishin, Emperor Zule, aims to conquer the galaxy and ends up in a conflict with Earth as a result. In an act aimed to eliminate the Earth, he sends a baby named Mars to live among humanity. Mars is accompanied by Gaia, a giant robot that utilizes a new power source strong enough to destroy an entire planet. Once Mars grows up, he will destroy the Earth by activating the bomb within Gaia. However, upon arriving on Earth, Mars is adopted into a Japanese family and given the name Takeru. Seventeen years later, Takeru has grown a love for humanity and he refuses to detonate the bomb as ordered by Zule. However, the bomb within Gaia is set to explode if Takeru were ever to die, which would ultimately result in the Earth's destruction. Takeru possesses psychic powers (ESP) and decides to join the Earth defense forces and becomes a member of the Crasher Squad (an elite space defense force) where he and his friends take a stand against the Gishin attack. Unknown to the Gishin, five other robots were created in secrecy along side Gaia by Takeru's father and sent with Gaia to protect Takeru. The five other robots are Sphinx, Uranus, Titan, Shin and Ra. Whenever Earth is in danger, Takeru is able to summon the five other robots to combine with Gaia form the giant robot Godmars.

Go Lion

Golion, a powerful sentient robot, abuses his great powers by attacking and killing creatures known as Deathblack Beastmen, boasting that no one could defeat him. A divine space being punishes Golion for his arrogance and abuse by seperating him into 5 different lion robots. In the year 1999, a group of 5 young men return to Earth after a space voyage, only to find it ravaged by nuclear war. After encountering the alien race known as the Galra, the 5 youths end up on the planet Altea, and learn that the 5 lion robots that Golion was split into are in hibernation in various parts of Altea. Somehow, they must reunite the lions and form Golion, the only hope for the human race.

Uchuu Majin Daikengou

Giant robot Daikengo flies through space to re-establish galactic peace; on-board prince Ryger, who ran away from his planet Emperius to defeat the menace out of his reign borders, in order to save his people; Cleo, corrupted prime minister's daughter, help him along with two nice little robots, Anike and Otoke. They fight evil Lady Baracross, leading invasion forces, with her assistant Roboleon, wearing a Napoleon style hat. Daikengo is the first robot with scuttles on his mouth. When he opens them, his vampire style teeth are shown and he can spit fire. (Source: Anime News Network)

Golden Warrior Gold Lightan

When a young boy called Hiro finds what appears to be a broken lighter in an empty field, it changes his life forever. This lighter is actually the Gold Lightan, a robot that fell to Earth from the Robot Dimension. When called upon to defend the Earth from Ivalda the Great's evil robots, Gold Lightan transforms into a giant super robot, known as the Golden Warrior. Gold Lightan joins forces with Hiro's and his gang, the One Pack Rangers to protect the Earth from the evil schemes of Ivalda the Great and his armored forces.

Space Knight Tekkaman

Tekkaman is just an average bright boy in his everyday life. However, modern science can turn him into a mighty space warrior. This becomes a reality when aggressive aliens come from space to invade our planet. Armed with a space lance, Tekkaman gallantly goes into action against the grotesque space creatures. During his battles he encounters a mysterious young man from another planet who helps him out whenever he is in danger. (Source: Absoluteanime)

Shin Tetsujin 28

Shortly after pre-teen Shoutarou Kaneda discovers his late father's legacy, a 60-foot-tall, 50-ton remote-controlled robot, he's put in charge of it. Shoutarou accepts the V-controller and duty that his father intended for the giant robot, Tetsujin: to fight evil and keep the peace. As the youngest member of Interpol, Shoutarou’s adventures take him around the world, under the sea, through time, and the deepest reaches of space. His mentors are Dr. Shikishima, his father’s brilliant colleague, and Inspector Ohtsuka, the sometimes buffoonish chief Interpol liaison, but in someways, Shoutarou is closest to his giant avatar, Tetsujin. Together, they battle various menaces, from mad scientists to pirates to ninjas to international criminals, all with their own unique giant robots, but the deadliest villain that Shoutarou and Tetsujin build up to is the Space Demon King, an alien so powerful that he threatens to swallow up the Solar System. (Source: Discotek)

Tetsujin 28 FX

Decades have passed since Shotaro Kaneda and Tetsujin 28 protected the world but evil continues to strike! It’s time for a new hero and a new robot, Tetsujin 28 FX, to protect the world! Masato Kaneda returns after mysterious vanishing a year ago to take up the reins of protecting the Earth along with his family and friends from the diabolical Neo Black Gang. With upgrades for Tetsujin 28 FX from Masato’s brilliant mother Yoko, along with Shotaro and the original Tetsujin 28 occasionally leaping in to help, can they stop the Neo Black Gang and all the other villains and rogue robots?! (Source: Discotek)