I just moved back into Manhattan and figured I need a serious lock. I bought the Kryptonite New York Noose. It weighs nearly eight pounds (3.5 kg)!
It might be overkill in some situations, but I'd rather not have my bike stolen. Any suggestions? Some have said the best way to use it is to "noose" the rear wheel between the seatstays and chainstays so the would-be thief can't steal the frame. Then put the padlock around the object you're locking to. I guess I should use a cheap cable to lock my front wheel to my bike.