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)

Muteki Koujin Daitarn 3

Souzou Haran was a brilliant scientist that was conducting research on Mars. He created a form of cyborg life with the ability to think for itself. These cyborgs, dubbed the Meganoids, soon ran out of control and killed Dr. Haran along with his whole family, save his youngest son, the 16-year-old Banjou Haran. Banjou escapes from Mars on a rocket with a solar-powered super robot called Daitarn 3, which was built with the special metals of Mars. Now eighteen years old and living on Earth in a luxurious mansion, Banjou fights against the Meganoids with the aid of his faithful butler Garrison and his two gorgeous companions Reika and Beauty. Together they must stop the evil Meganoids which aspire to turn all humans into cyborgs and thus "improve" the human race. (Source: AniDB)

Patlabor the Mobile Police

In the future, advanced robotics has created heavy robots ("labors") for use in a variety of functions: construction, fire-fighting, military, and more. However, though the robots are only machines, their operators are also only human - and humans sometimes turn to crime. Since a heavy labor unit can be a dangerous weapon, the police of the future are set to fight fire with fire, using advanced patrol labor units, "patlabors". This is the story of the Second Special Vehicles Division, a motley crew of patlabor policemen and -women doing their best to fight crime and live a normal life. (Source: Anime News Network)

Dai-Guard

Thirteen years after their sudden disappearance, an alien race known as the Heterodyne resurface without warning. To combat the Heterodyne, three office workers from the 21st Century Security Corporation operate Dai-Guard - a giant robot no longer regarded as an oversized paperweight. Unfortunately, Dai-Guard is somewhat obsolete and in disrepair. It's a tough job, but salarymen can also save the world. (Source: Anime News Network)