I'm shopping for a new bicycle U-lock. If a regular U-lock is not strong enough for you, there is a product line known as the Kryptonite New York U-Lock. These are extra heavy U-Lock made of hardened steel. Presumably people who need extra security would go for this. It also cost about double compare to a regular U-Lock.
I find it amusing that the product line is called New York U-Lock. Customers apparently know exactly what New York stands for, a high crime, dangerous kind place where you must heavily lock down your properties or it gets eaten alive. The mayor of New York must gets really offended by their branding :)