I'll start off with the more serious stuff that's on crunchyroll The Irregular At Magic High School - it has a alot of awesome fights in it and a bit longer than typical anime
Attack on Titan - A very serious anime. It starts off kinda slow. It different from a lot of other anime
Sword Art Online
Log Horizon
Broken Blade - A pretty decent mecha anime. it's episodes are kinda structured weird.
Fate/stay night
Akame ga Kill!
Blue Exorcist
Fairy Tail
Oreimo - It's a comedy but it's extremely funny. It's hard to turn away from after you start to watch it.
If you're watching Knights of Sidonia then most likely you have access to netflix, Here's some stuff that's on there that I recommend that you watch.
Spice and Wolf - a anime that requires you to think and pay attention. there's little action in it though.
Blood+
Deadman Wonderland
Soul Eater Magi: Kingdom of Heaven
Psycho-pass Fate/Zero Here's some stuff that's really good but not on either one.
Here's two that aren't on either streaming service but keep an eye open for 'em.
Elfen Lied
Sword of The Stranger - It's a full feature anime film. Has the best sword fights.
Crunchyroll is free if you watch it with commercials by the way.
