I mean, you could always read Dark Victory, the sequel to The Long Halloween. It's not as good as The Long Halloween, but I'd still says it's required reading for Batman fans
You haven't read Year One? That's also required reading
I liked the Geoff Johns Batman: Earth One books. It also looks like those books are the inspiration for the upcoming Matt Reeves Batman movie, especially in their interpretation of the Riddler
The Knightfall Trilogy is a classic. That should definitely be on your radar
And while it isn't a typical Batman story, I loved the bit of Gotham Central I read. Didn't finish it because my library doesn't have the whole series, but I loved what little I read.