You have to love Two-Face's story arc in Arkham Asylum. That is just a great book all the way around.
Here are some of my personal favorites for Batman trade paperbacks/graphic novels (in no particular order):
The Dark Knight Returns
Year One
The Killing Joke
Year Two
Son of the Demon
The Cult
A Death in the Family
Arkham Asylum
Night Cries
Gotham By Gaslight
Holy Terror
The Long Halloween
Dark Victory
Batman/Dracula: Red Rain
Blind Justice
Strange Apparitions
Hush
Poison Tomorrow
Batman Illustrated by Neal Adams Vol. 1,2,3
Batman Archive Editions
Dark Knight Archive Editions
Showcase Presents: Batman/The Brave and the Bold Editions
There are a ton more, but these are a nice start for anyone getting into Batman. I always look for good writer/artist team-ups like Denny O'Neil/Neal Adams, Frank Miller/Klaus Janson, Mike W. Barr or Jim Starlin/Jim Aparo, Alan Grant/Norm Breyfogle, Jeph Loeb/Tim Sale, Steve Englehart/Marshall Rogers, and of course, Bill Finger/Bob Kane.