My collection comprises of the following:
Batman Vs Predator - the best crossover in any medium, ever, IMO
Batman Vs Predator II: Bloodhunt - the closest a comic has ever come to replicating the flow of an action movie
Batman vs Predator III: Blood Ties - solid but tepid
KnightFall Part I: Broken Bat - essential reading
KnightFall Part II: Who Rules the Night - ditto
KnightFall Part III: KnightsEnd - rushed and not as good as the other two
Batman & Dracula: Red Rain - super gothic horror, the best ElseWorlds book
The Batman Chronicles Vol 1 - classic stuff, amazing how few posters have read the original Batman stories and think Frank Miller invented Batman
A Death in the Family - classic stuff
A Lonely Place of Dying - Oft-overlooked, Tim Drake becomes Robin
The Long Halloween - not quite the masterpiece it's percieved as, could be told in 1/3 of the length and most of the supervillains are superfluous
The Collected Adventures Vol I and II: wonderful stuff based on the animated series of the 90's
No Man's Land vol I - I'll take NML over War Games any day, even though they're really rather similar
The Killing Joke - best Joker story ever
As The Crow Flies - simple story padded waaaaaaaaaaay beyond it's length
Hush Vols I and II - Amazing art. Forgettable story.
Broken City - Batman comics got really grim and depressingly gritty in the early 2000s, and this is the most extreme example of that. Almost Batman in Sin City.