Reddit mentions of Smead Self-Adhesive Poly Pocket, Business Card Size, Clear, 100 per Box (68123)

I use 48"w x 18"d x 74"h wire shelving, 5 shelves, with 1/4" wood liner shelves. Each unit holds 25 short boxes, and they are easy to get on and off the shelves. I just added a second shelf unit tonight so I have a picture handy:
http://imgur.com/BTytifp

Edit: Here are the shelves I use:

• Lowe's, $74.98.
  
• The chrome ones are currently on sale for $59.98.
  
  I can't find a link to the wood I use for shelf liners, but it's fantastic - it's a reddish-stained smooth plywood which comes in a 4'x8' sheet for about $14 - it's sold as 1/4" but it's closer to 1/8". I cut it to 17" x 46.75" shelves, and then cut off about 1.25" inches off of each corner so that the liners sit right into each wire shelf. Short boxes slide in and out very easily.
  
  While I'm at it, I highly recommend using business card holders and printable business cards to label your short boxes, it's really improved everything for me... recommended:
  
  
• Business card holders
  
• Printable business cards
  
  I also use a sharpie on the backs of old business cards to help organize whatever boxes I'm using for filing.

Would tape not work on the wall? You could put one piece of tape on the top, and if you need to scan the back you can just flip it up. You can put a backing board up to tape the coupons to if you're worried about using tape on the wall. Maybe something like a piece of plastic put up with poster tack.

Or, just use poster tack for the coupons. It's reusable. You won't be able to flip them over though.

Other ideas:

• clear business card sleeves
  
• binder clips
  
• the magic of command hooks