Method #1: Mirror clips...2 on the bottom edge of the glass, one on the top edge

Method #2: The edges were a mess and it's an inexpensive/generic slot glass that I didn't want to pay to frame. Bought some sticks of wood from the doll house department of a local craft store, got out the exact-o knife, and made a frame. I seem to remember using a black marker to "paint" it!

Method #3: Easels on top of book/display shelves

Method #4: Measure carefully and have frames made (these were from Hobby Lobby)