I'd definitely second Gurren Lagann, Fullmetal Alchemist and Code Geass. Another couple goods ones would be Samurai Champloo, Cowboy Bebop and Psycho-Pass.
Here are some of my anime recommendations, they are not strictly action having mixtures of Fantasy and Sci-Fi elements. I'm not good at writing plot summaries so don't just judge these from what I write about them go check them out yourself and I'll probably add more later. Psycho-Pass: This is a very though provoking futuristic/crime series. Set in the future people are assigned a Psycho-Pass rating which indicates their threat level to society. Without giving too much away this is about the life of an Inspector named Akane Tsunemori and her interaction with the Sibyl System, the entity pretty much determines the fate of a person. Through her adventures she discovers more about Sibyl including the truth behind it's existence and the realisation that it's judgements are not always accurate. Full Metal Alchemist (Brotherhood is much better than the original 2003 anime in my opinion): Follows the story of some young brothers who use alchemy to try and bring their dead mother back to life, human transmutation is considered a taboo and a result of them "playing god" one of the brothers lose a arm and a leg while the other loses his whole body - he then has to have his soul bound to a suit of armor. The main story arc is about them trying to recover their bodies and finding the deeper secrets of alchemy including that of the philosophers stones and the homonculi (artificially created humans). D.Gray Man: One of my favourite animes of all time. D.Gray Man is about a exorcist by the name of Allen Walker who joins up with Black Order to fight Akuma, deadly machines powered by human souls and dark matter. These demons are created by the Millennium Earl who is the head of the Noah clan. To sum them up over 2000 years ago the original Noah clan fought the exorcists, they lost but the world was still destroyed by the event known as "The Great Flood". All human decedents have the Noah gene within them and when one of the members die that exact memory awakens in a random human. Exorcists are the ones chosen by God and have a special power depending on their "Innocence" and this power is the only weapon effective against the Akuma and Noah. Allen and the rest of the exorcists must stop the Millennium Earl and the Noah from bringing about another apocalyptic event.
One punch man(season 2 sooo. Bb) Hunterxhunter(unknown) Jojos bizarre adventures(ended) Tokyo ghould(expecting new season) Mobile Suit Gundam: Iron-Blooded Orphans(still running)