If you are looking for a Sci-Fi action anime then I suggest you try out out:
[spoiler=Code Geass: Lelouch of the Rebellion]
An anime about the son of the leader of the Holy Britanian Empire, he starts a rebellion in Japan which is occupied by Britanian and is now known as area 11. This anime is mecha, military and supernatural. 2 season with 25-ish episodes, the dub is good. There is also a movie that I haven't got around to watching yet but that one isn't dubbed.
Then there is these classics:
[spoiler=Trigun]
An anime about a legendary cowboy with a 60 billion double dollar bounty on his head in a desert world with what little is left of humanity. 1 season with 25 episodes and a movie, the dub isn't that great but its alright.
[spoiler=Cowboy Bebop]
Follow the crew of the spaceship Bebop a spaceship that starts off with a duo of an ex-police agent and a resigned member of a syndicate, later joined by 3 more crew members this one plays out in space as the bounty hunters try to scrap together some money. Great fight scenes and also great if you enjoy Jazz, the intro is still one of my all-time favorites. 1 season with 26 episodes and a movie, just like Trigun the dub isn't that great.
but the 4:3 resolution might drive you away.
And finally I have this one for the less actiony and more mind twisting anime:
[spoiler=Steins;Gate]
I can only describe this with two words 'Time' and 'Travel'. Starts of slow but by episode 5 you will not be able to take your eyes off the screen. 1 season with 25 episodes, all of the dubbed pretty well.
I also have some more suggestions if you don't only want sci-fi so feel free to ask .