| Speed Grapher is definitely one you want to check out.
Code Geass is a decent choice as well if Darker than Black is serious enough for you.
Romeo X Juliet falls into romance side a bit, but I'd definitely lump it into the action/quality of the ones you listed.
And on the RxJ note - Gankutsuou, the same company's Count of Monte Cristo remake.
And for something completely different:
Major. It's a baseball anime. Yes, I'm dead serious in recommending this. It's currently in its third season and follows a guy from his childhood in Japan to playing in the US (right now it's in the highschool arc). There's not much in the way of romance in it and all and there's some rather fucked up shit the guy goes through throughout his life.
And on another different note:
Nodame Cantabile. It's a series about a guy working towards being a conductor and it is a pretty amazing change of pace from every other type of series. It also has some incredible compositions played in it.
__________________
 |