Definitely agree with Cyrus. Top Ten and Swamp Thing are great reads.
But here is an unsung great Alan Moore comic.
In Batman Annual #11 famed writer Alan Moore explores the growing insanity of Preston Payne and his homicidal obsession over his wife Helena, who is actually a department store mannequin. Yes, I know it sounds lame but it isn't. Moore's words of love and jealousy is eerily beautiful and would gain the sympathy if the most cold hearted comic book reader. This is a must read to any comic fan, Batman or otherwise. I dare say it, this issue is even better than the famous Killing Joke.
Here are some of my favorite quotes from the issue.
"Why do men do the things they do? We are so weak and cowardly...perhaps women are right to despise us. In love, we behave like children lost in the dark. We close our eyes when we kiss, afraid lest we should glimpse the awful truth...that we are not loved. That the object of our affection is cold and unfaithful...why? Why do we never see the treachery in their eyes...until it is staring us right in the face?"