Case for ZS20
That's a tall order. I've bookmarked a half dozen or so case options for my ZS20, but none of them had a magnetic catch.
I'm sure I'll wind up with a couple to handle different occasions, but I just bought a LowePro Santiago 20 hard case pouch for it. It's perfect as a small, minimalist case for your belt, and I really like the fact that's its hard. I can throw it in my work bag and not worry at all about it getting squished or banged around. It doesn't fit a 2nd battery, but will accommodate spare memory cards.