Not to sound like a sketchball, but I have another hobby, that is lockpicking (don't worry, I only use my skills for good!) but you'd be surprised how easy most locks are to open. i see people using regular padlocks + a chain to lock up bikes thinking that a big "master lock" is secure... guess again- it's not. I can open so many master locks in less than 1 second with a pick and a tension wrench... I wish I was kidding.
I use a kryptonite u-lock, not sure which model it is, but it's the middle sized length, and pretty beefy, about 5 lbs. (also makes a good weapon, had to use it to keep some dude from jacking my bike once :-\ )