I have a Kryptonite NY Fahgeddaboutit mini U-Lock and it is a beast. I'm pretty sure it would take a fire department to break it off my bike. However, it does weigh a ton.
EDIT: This one ->
http://www.bikeradar.com/gear/catego...dit-mini-16565
Last edited by thegnome; 10-11-12 at 05:04 PM.