My first comic book was the Dark Knight Returns Volume I published by Editorial Vid, and to this day is a comic that i re-read once a year. Try standalone stories: one shots and miniseries are a very good entry-point to larger characters and concepts. I enjoying reading Condorito as a child, and i remember an horror anthology published in Chile called Doctor Mortis. Here's in Argentina, there was a boom of comics in the 40's and 50's with publications like Hora Cero (home of El Eternauta) and many humor publications like Rico Tipo (if you know artists like Shane Glines and Bruce Timm, their style is very influenced by the style of Guillermo Divito's and his way of drawing women's).
Anyway, here's some recommendations:
DC/MARVEL
Batman: Year One
The post-crisis retold of the origin of Batman, by Frank Miller and David Mazzuchelli, a classic who stood the test of time and a first step in a resurgence of the noir genre in the mainstream comic books of United States.
Batman: The Sword of Azrael
Batman goes beyond Gotham City to stop a new vigilante with flame swords called Azrael (there's some Da Vinci Code mumbo jumbo in this one, with templars and things like that). This comic embodies some of the excess of the nineties (Azrael is a sort of Spawn in reverse), but with a touch of sophistication. Dennis O'Neil (one of my favourite comic writers, thanks to The Question), Joe Quesada and Kevin Nowlan are a perfect match.
Superman: The Man of Steel
Classic revamp of the character for the post-crisis version done by John Byrne, one of the most prolific authors of the 80's. The modern versions of Lex Luthor and Lois Lane starts here, followed by an excellent run in the Superman and Action Comics titles, with Byrne and other authors like Marv Wolfman, Jerry Ordway, etc.
Punisher: Circle of Blood + Return to Big Nothing
The team of Steven Grant and Mike Zeck are a perfect match, and this first volume of the Punisher is a classic reccomendation if you want to begin reading the character (besides modern runs like the Ennis one). Followed by a regular series with excellent moments until the number 50. I still have the issue 75 (with a Simon Bisley back-up), one of the first comics i ever read and the first comic who i tried to read in another languaje as a teen.
Punisher: Assassin's Guild + Punisher Kingdom Gone
Two Marvel Graphic Novels, Zaffino is the artist of both. The first is written by Mary Jo Duffy (the first woman writing Frank Castle) and the second is by Chuck Dixon, both are two Punisher Comics who i re-read every year (i only have the first in physical form).
INDEPENDENT PUBLISHERS
Winterworld
Published by Eclipse Comics, an history of survival in a post-apocalyptic world. One of Zaffino's best works.
Seven Block
An one-shot by Dixon and Zaffino published by Epic and Dynamite, an horror story with a sinister and macabre mood on every panel, it gives me the chills.
Mister X
Published originally by Vortex: the protagonist is Santos, an architect who can't sleep, trapped in a city full of insane people. The influence of this comic is notorius in things like Batman: The Animated Series (one of his artists -Paul Rivoche- did backgrounds for Batman Beyond, Justice League and many DC Animated Series) and the movie Dark City. Dean Motter is the writer and sometimes the artist, with collaborations by the Hernandez Bros, Bill Sienkiewicz, Seth and others. It's a great comic, full of up's and downs, but i enjoy it (especially in his most weird moments, like the Milligan Special Mister Insect). I suggest the two miniseries of Terminal City by Motter and Michael Lark as a follow-up.