Choujuushin Gravion

If you thought Gravion was good with the meka's combination and a bit of a story line wait until you watch Aquarion. Like Gravion, Aquarion meka's are based on combination, however Aquarion has a bit more of a story line behind it ^_^ 

If you seek similair feel of cheesy quazi-harem with minimalstic plot and a big chunk of fanservice in mecha setting - here you go. 

Like Tri-Zenon, Gravion is a series where a group of unlikely people are gathered together to pilot a giant robot in order to defend the world against an alien invasion. Even though its crew is not as over-the-top as Tri-Zenon's, they're still quite a bunch, and as a result there's plenty of comedy ensured (ranging from "physical exams" to crossdressing to overdone dramatic posing), yet still with plenty of action. 

If You liked Giant Robots Fightig form the human world this is another good anime, epic, carismatical caracters and a lot of mecha 

Two shows for fans of big, honking, sugoi dekai... robots. Hot blooded manly mecha action with big robots, shouting finishing moves, and girls with absurd, uhh, personalities... These two anime are brothers in spirit, and I can't see why a fan of one wouldn't enjoy the other. 

The story are both about protecting the Earth from Aliens. Both mechanic design are by the same person