Crisis on Infinite Earths - Decades later and still holds up as one of the best crossover events. I wish we lived in a world where every comic character who died got to go out like a G the way Supergirl and Flash did.
The Legend of Wonder Woman - A more recent one. I'm a huge WW fan, so I've read about a dozen different takes on her origin. This is easily the best one.
Grant Morrison on The New X-Men - Despite my avatar, I actually can't stand the X-Men most of the time. But that Morrison run was some good shyt.
Black Panther: The Client and Enemy of the State - Already mentioned, but if you haven't read any Black Panther, pick these up.
Black Panther: Panther's Rage - First arc of Panther's first solo series. Underrated classic.
Grant Morrison on Batman and Robin: Not a huge Batman fan, but Grayson and Damian were the GOAT Caped Crusaders.
Superman for All Seasons: I jump between this, Secret Identity, and All-Star as my favorite Superman story. All Seasons is the one I always find myself going back to though.
I Kill Giants: Beautiful story about being young and dealing with depression, loneliness, and accepting death. I'm working on becoming a full time teacher (only a sub now) and this is a book I would love to teach someday with older students.