This isn't a decorative suggestion, but I use the plastic clamshell containers from the Crumbs cupcake chains for starting seedlings. The individual cupcake-sized divisions and the lid make it a perfect mini greenhouse.

That will rust the dickens out of your muffin tins. Best to use them for muffins, I think.

These are cute, and I have some crappy old muffin pans that would work great.
I'd recommend putting little felt squares or something on the bottom, because even if you don't care about the pans you could hurt whatever surface they're on. Speaking from experience using old film reel canisters as plant saucers.