Batman - The Dark Knight Returns - The birth of the Goddamn Batman. Love the art, the tone, the Super-stooge, the new Robin, the retirement of Gordon, The end of the Joker. All of it.
Captain America - Winter Soldier. Never the biggest Cap fan outside of Avengers but this was awesome. Made the return of Bucky rock.
Avengers (Any incarnation) - Under Siege - Action, action, action! The fall of Avengers Mansion and the brutal beating of Hercules. Awesome fights and a great overall story.
Teen Titans (Any incarnation) - Judas Contract - What else is there? The titans are the junior justice league, they mostly suck. Dethstroke rocks though.
Hulk - Um the Two Part story where he fought both teams of Avengers. What other choices are there? An out of control Hulk fighting all the Avengers at once and holding his own. When he was using Samson as a battering ram was great too, the pony tail wearing poser.
Superman - Man of Steel - The beginning of when I could read DC comics and not have all the stupid Golden/Silver age crap to deal with. Great art, a and a great reboot of the character. Too bad its all back now, all the crap, all the extra Earths, all that SHIT!
Spiderman - The Death of Gwen Stacy - The most powerful Spidey story and great art by Gil Kane. Ownage.
Wonder Woman -
I the George Perez reboot was as close as she came to not sucking.