I live in NYC and commute with an expensive bike. This is what I use:
ABUS folding lock and ABUS U-lock
I find ABUS locks to be far superior to Kryptonite. Master doesnt have a reputation of being too safe.
I also use pitlocks on the front wheel and the accesories are secured by Atomic22 fastners. A bit overkill, but I love my bike!
Spend as much as you can on the lock, dont skim on this very important accesory.