On the same shelving unit I have galvanized metal boxes that hold all my fabric samples, so I opted to make galvanized metal tags to match. These inexpensive metal garden markers came with one edge already bent, and I used a metal ruler to bend the opposite edge down as well.
I put a dab of gorilla glue on the back (careful not to put too much because the stuff tends to expand and you don't want it oozing out around the edges) and pressed into position on the box. *Tip: set the box on its back as the glue dries so the label holder doesn't slide down with gravity...a couple of mine did that when they dried.
For the actual labels I just used paint chips, which gives you a dizzying array of colors choices. I like that my labels tie in with my "Lemongrass" accent wall.
The label holders wound up costing about 30 cents apiece, and the boxes were only $5 each, so for a very sweet price I love this tidy and cohesive look for storing magazines in an office setting!