>>1536379New x-men by Grant Morrison. It goes down the hill in the last arc but is consistently very good all through out. Also, you don't need to read another 30 titles and 120 crossovers to understand it.
Weapon X by Barry Windsor Smith. Dark and slow boil shit. Very good if you get into the pacing. It's an storyline but you might call it only a graphic novel.
The ultimates by Millar and Hitch. Although Millar is an acquired taste. Also, it's not the main marvel universe, but who's counting?
Immortal Hulk, quite nice.
Daredevil: born again by Frank Miller and Mazzucchelli. More an story arc than a story line. Very good.
I could rec you some classic stuff but I think you can start with those.