1. The Preacher series
An amazing series with a combination of action, romance, friendship, vampires, religion, and angels. It probably offends as many people as it fascinates. Full of violence, vulgarity, and ideas that would be sacrilegious to a lot of people. I loved whole nine-volume span.
2. The Sandman series
Another long series, written by a great writer (Neil Gaiman) with a lot of mythology thrown in.
3. 30 Days of Night
Vampires in Alaska. The art was so different from anything I had seen before and just wonderful.
4. The Sojourn series
One of the lines from Crossgen that was cancelled about a year or so ago. The story was unfinished at four volumes but had amazing, full-color art and a great story about a female archer who's family was killed and who went searching for revenge.
5. V for Vendetta
One of the amazing things about this book by Alan Moore was that you never see V's face. He always wears a mask and I enjoyed the mystery of his character.
6. The Red Star series
A fictionalized story of the Soviet invasion of Afghanistan in 1979, but so much more than that. I love the military viewpoint, the absolutely amazing art, and the injection of sorcery into a modern setting.
7. The Sin City series
Gritty and violent, populated with a huge cast of characters. The basic black and white art with just a few touches of color makes the story itself the most important thing in this series. I thought the movie was great and an excellent adaptation of the first three books.
8. The Ruse series
Ruse was another Crossgen series. It has a connection to Sojourn (all of the Crossgen stories are connected), but you don't need to read all of the stories to understand what is going on. Part supernatural story and part detective story, Ruse is set in Victorian England, with a Sherlock Holmes type of detective and a female assistant.
9. Road to Perdition
I saw the movie before I read the graphic novel, but the book itself was amazing in its own right. It was very different than any of the graphic novels I'd read up to that point, and I enjoyed the Depression-era gangster setting.
A huge book that tells a semi-autobiographical tale about a young man's rough childhood, and family, friendship, and first love.