The Onguard Bulldog Mini U-Lock is the best lock that I’ve found and needed (there are stronger locks, but not for this price). It’s fairly cheap ($21.99 here) for a lock of its durability.

The lock is made of hardened steel (covered in rubber and vinyl to protect your bike), so it does add 2 lbs. 2 oz. to your bikes weight. The lock uses laser-cut keys, including a lit key for the nighttime (although I personally never have to bike at night).

I have a feeling that if someone was able to break this lock, or any Onguard, or Kryptonite lock, your bike would be so mangled it wouldn’t matter. It’s going to take a lot of force, or power tools, to get one of these open without the key.

There really isn’t too much to say about this lock, other than it is the one I picked, and it has worked really well for me so far.