I am on the hunt for a used or vintage round mirror. Here's my favorite one so far, the only problem being that it would have to be shipped from the UK, making it not so eco-friendly. Otherwise, it's pretty and simple, not to expensive and is 60's vintage teak. It's from
H is for Home.

Here's a pretty convex one from
Sutter Antiques that has no listed price.

This Roger Capron ceramic one from 1968 is also cool from
Mary Ann Lembo.

Here's a slightly strange bumpy cork one from
Avant Garden. 
I just repainted most of the walls in my kitchen Benjamin Moore's
Aura line "Yellowstone" mustard yellow to get rid of the pumpkin-y orange that has been there since summer 2005 (see the shelf wall with other color in photo here). I want something new to hang on the wall here. If I can find a round mirror, it would be hung high above the stove in the empty space for good feng shui purposes.

Next stop, ebay....