Yale Y220/61/123/1 Laminated Steel Padlock with Vinyl Cover and Brass 5-Pin Key Cylinder, 2-1/4-Inch Wide

A very solid, well made lock. The vinyl cover makes it both durable and less likely to damage its environment. The dual ball bearing design makes it immune to shimming (a simple method to open ordinary Master locks in seconds). The 5-pin cylinder could still be picked, but it provides a much better barrier than your typical "toy" lock. Note that with the vinyl the shackle is somewhat thicker than average and may not fit small openings. I wouldn't bother with anything less secure than this lock. Consider this one, or the Y130 if you want something with a guarded shackle.

I needed some locks for my car trailer. I wanted something with a cover so it wouldn't rust and seize while outside. These are completely encased and even seal on the shackle. Lock mechanism is brass. Comes with 4 keys.Update 6/2013: In spite of thoroughly lubricating before leaving these locks on the trailer outside all winter, the first time I tried to open them this spring they had all seized. Two I was able to loosen up again after lubricating but the 3rd was stuck and I ended up breaking off the key. Finally I had to cut the lock off. So while cheap, I guess I got what I paid for...