Smith & Locke Stainless Steel Waterproof Disc Padlock 80mm - Free C&C

Worth getting for outdoor use as the rust resistance is very good.

As others have said, for somewhere like a shed the wooden door or weak hinges can easily be ripped off anyway so an expensive lock is pointless (edited)

Good for gym

I've a couple of these on a shed - they seem solid enough and have only the smallest amount of tarnish on the back after 18 months or so.

The annoying thing I find about the style of these is that you need the key to lock them back up. This can be quite annoying - even more-so when you have two that aren't keyed-alike.