Dont be a wuss, I have the NYFU which is apparenly the "best" U lock around, in that it can withstand cutting for around 5 minutes, It weighs alot, but I also dont have to worry too much* about my bike (*too much, I am always a little worried, sometimes i wake up in cold sweats, but then i just roll over and give my bike a little caress and tuck her in).

the NYFU is great, if you are locking in a city, it goes around the frame, through the back wheek and tightly around a parking meeter, my favorite locking medium, not many people will cut a parking meeter), though it does weigh a ton, but just dont have access to a lighter one, and you will never know!