Run, do not walk, to Target's One Spot area! I found these metal plant markers in the One Spot clearance for 30 percent off, which means I got a package of 5 metal plant markers for just 70 cents each. I bought my Target out of them--about 20 packages. Each package comes with a small permanent marker, too, so I have plenty for future marking! I stopped in another Target today, and their One Spot clearance is at 50 percent off, but no plant markers.
Usually I use popsicle sticks or something similar, but this was too good a deal to pass up. Plus they are easier to see (they shine in the sun!) and are a little more permanent. Who doesn't love a good gardening deal!