I don't do many shows, so the displays I use are usually home-made and inexpensive. Since we are in the middle of show season, I thought I'd re-post my DIY earring display. Here is the original post.
The earring cards and hangers were a great investment. Each card has a little plastic back 'hook' so I was able to hang them on ribbon.
The hooks are adhesive and attach right to the back of the card you want to hang:
Photobomb by Marnie:
I've also found that baseball trading card stands make great earring displays. I found these on EBAY:
They're the perfect size to display earrings as well as my business cards:
Good luck in all of your shows!