Tengen Toppa Gurren Lagann

This is an anime I was told to watch aaaages ago for it's utter madness and it definitely matches to that. In the distant future humans are forced to live underground and must constantly drill deeper to avoid the slowly decending ceiling. But Kamina isn't like every one else, he's been to the surface with his dad and now he's determined to get back, with Simon's help. However after their plan fails another means to get to the surface arrives and Simon and Kamina are free to roam the surface with Yoko, the sharp shooter who enables their escape. Now their on a mission, to stop the mechas called Ganmen at the very root to save the underground villagers from the earth quakes they cause. Simon controls the head of a Ganmen named Lagann while Kamina controls a body called Gurren. To fight off the Ganmen Simon and Kamina must combine to form Gurren Lagann with their fighting spirit to produce any number of drills. It's all one big joke really. But it has the boobs and the mecha to interest a large number of males even with the ridiculous speeches, pointless transformation scenes and inconsistent plot.

Neon Genesis Evangelion

That's right! I've finally got round to watching the anime of it!! Although I doubt you guys remember when I bought the Neon Genesis Evangelion manga only to discover that it's actually meant for people who had already watched the anime.

Quite honestly I don't think that me watching this anime was that smart, since I'm no mecha fan and I'm not a fan of older art style. But still I am quite impressed by Neon Genesis Evangelion! It's certainly not my style of anime and I'm not going to join the massive buzz surrounding it, but for what it succeeds at being what it is!
It mostly revolves around the high-tech military organisation Nerv. Buried deep under New Tokyo 3 Nerv holds some of the strongest weapons known to man which are used to defeat the powerful aliens/robots called Angels. Nerv's strongest weapon is a giant meccha suit which can only be controlled by a select few. The pilot has to be 12 years old and be able to synchronise effectively with the robot. They are called Evanglion's or Eva for short. Shinji Ikari is one of these select few and is called in to be a pilot by his father, head of Nerv. The story is then mostly about Ikari being a seclusive teenager with pointless meccha fights put in every episodes.

Full Metal Panic!

My friend reccomened this to me aaaaaages ago but I only just picked it up. As the name suggests, it's a Shonen mecha. The very opening scene is a couple of soldiers in 'arms slaves' (Robot suits) blasting tanks apart to save a pretty girl. Is their anything more Mecha than that?
But it seems to then lose it's mecha title for the next 4 or 5 episodes. Sousuke, one of the Mithrils top soldiers, is set an important misson: secretly guard Kaname Chidori, the seemingly ordinary High School girl. To do this, Sagara Sousuke must transfer to Chidori's High School, while his comrades - Kurz Webber and Melissa Mao - follow her around in slightly more invisible methods. But the problem is, Sousuke has never attended High School. How was he supposed to know that carrying guns around school is against the rules? As such he becomes known as the military geek.
However, when Mithril defeat the enemy base does Kaname need her body guard any more? But Sousuke still has a school trip to attend and it's a good thing he does as well becasue as it turns out the enemy ended up hi-jacking the plane to kidnap Kaname. The Mecha returns, tanks everywhere, Slave arms fighting face-to-face and explosions EVERYWHERE! Sousuke has been ordered to protect the hostages over Kaname, but what about all those memories of Kaname? It's a heartwarming tale of over-coming challenges for your friends/lovers/mission objective.