I was a bit of a comics nerd when I was younger, but I never read any Batman. I was more of a Marvel guy and I said before the only comic I really collected was X-Men. So when I came across one of those lists a while back about the Top Ten Batman comics, I decided that would be a good starting point to get into The Dark Knight.
Batman: Year One by Frank Miller
Year One has the added bonus of being a huge source of inspiration for the Chris Nolan Batman movies. The story follows a young Bruce Wayne as he first puts on the Bat-mantle. Since he's just learning the ropes, Batman makes a slew of mistakes and is hunted by Gotham PD. In a trademark Miller move, he made Selina Kyle a prostitute before she becomes Catwoman.
Since this is a comic, I'll comment on the art. It didn't really do anything for me. It wasn't as over the top as Miller's The Dark Knight Returns and it wasn't as full of energy and awesome visuals as his Sin City.
The real hero of the story is Jim Gordon; the sole honest cop in a corrupt department. He is a truly fleshed out character, full of conflicts. The rest of the story is well known (now), and didn't leave me breathless.
The Long Halloween by Jeph Loeb and Tim Sale
Chris Nolan pulled elements from this story for The Dark Knight and rumors for his third Batman movie hint that he might pull some more from this book. There is a serial killer on the loose, and he's taking out members of Carmine "The Roman" Falcone's crew. Each month, a murder is committed on a holiday using the same type of weapon (a .22), leading the killer to be dubbed "The Holiday Killer". Batman, Gordon, and District Attorney Harvey Dent team up to take down Falcone and apprehend Holiday.
I liked Tim Sale's artwork much better. His Batman was full of menace and his villains are top-notch. The only complaints I have are his Harvey Dent and Bruce Wayne are kind of generic, handsome, white guy-ish. I had a hard time telling them apart. Luckily, Bruce Wayne isn't in the story much.
Loeb was obviously influenced by The Godfather movie trilogy, but it helps the reader with a little shorthand to get pulled into the story quicker. I also enjoyed the relationship between Batman and Catwoman in this book.
If you remember the phrase "I believe in Harvey Dent" from TDK, this is where Nolan picked it up.
I believe in Batman.