Contagion, Cataclysm and especially No Man's Land are a MUST READ for anyone looking to get into Batman. It's the transition between old Gotham City and new Gotham City.
The Long Halloween isn't a must read, but I highly recommend it because it tells how Two-Face came to be. Very emotional and tragic story.
Tower of Babel is quite possibly the best JLA story ever.
Haunted Knight is very enjoyable, also.
Batman in Hong Kong is worth the buy if for nothing else than the artwork.