Code Geass - a prince hiding as a student gains the power to control people's minds and uses it to create a world revolution by creating an organization named the Black Knights, starting in Japan
Gundam 00 - a former child soldier becomes a pilot for an anti-war terrorist organization known as Celestial Being and uses his mecha to change the world and end war
Gundam SEED - a high school student is forced to pilot a mecha to save his friends from an enemy attack and joins a ship named the Archangel to end the war
Gundam AGE - split into 3 stories, first is about a young boy who built the only mecha that is able to destroy an unknown enemy; second is about the first's son and his friendship with an enemy soldier; the third is about the second's son and him trying to end the war against the unknown enemy
Gundam Wing - a mysterious boy is sent to destroy military bases on Earth by orders from an unknown organization and is seen by a girl who he then proceeds to try to kill
After War Gundam X - after a great war, a scavenger meets a girl who he saves and eventually finds a mecha which he learns to pilot and then joins the crew of a ship named the Freeden to save others like the girl
Gunparade March - a boy is paired up with a tough girl who is the daughter of the mecha creators and develops a relationship with her while trying to save all that remains of humanity
Full Metal Panic! - a young military soldier is assigned a mission to become an undercover high school student to protect a girl from terrorists who seek something that only she knows
Heroic Age - a boy born in an abandoned planet has the powers to become a mecha and is the only hope to end a war
Halo Legends - several 1-episode stories based on the Halo games
Iron Man (2010) - Iron Man in Japan
IS: Infinite Stratos - the only boy to ever pilot a mecha is accepted into a school and trains to become stronger for the tournaments but eventually has to fight a mysterious mecha
Macross Frontier - a boy who looks like a girl takes a mecha and fights off aliens to protect a girl who becomes an idol rivaled to the galaxy's greatest idol
Give these a try:
Susei no gargantia - beautiful animation, and world.
Macross Frontier - great music in this
Fafner in the azure - good sense of tension in the anime