This is hard, I couldn't really be bothered picking three. so much depends on my mood, phases etc.
DKR is absolutely on a level of it's own, no question there. Gushing, grovelling, DKR fanboy.
DKSA - severly under-rated, evidence of MENTAL ******ATION in general fanboy community. I find this consistently enjoyable.
All Star Batman - when it's all finally released the ASBR tpb's will be pretty alright I think. I'm counting this as an eventual body-of-work, not just issues 1-8 whatever.
The Cult - Hilarious, bewildering, Batman attacking strangers for food, Jason Todd slapping Batman around. I think of it as the forerunner to ASBR
Batman Black & White - All volumes. I'm not picking a standout right now but generally I love the BW tpbs and the short stories that appear in single issues. A higher standard of writing and experimentation.
The Killing Joke - If I had to pick only one from the obligatory classics (Arkham Asylum, Long Halloween, Year One, TKJ) then it has to be this.