Clear deli boxes and other number 6 plastics can be used as "shrinky dinks." Write on them with a permanent marker and then use an oven or a heat gun (not a hair dryer) to shrink them. The shrinking process helps the permanent dye ink last a little longer, although it's definitely not a forever label outside in the weather.

I've been thinking about using dog tags and hammering the name onto it using:

That would be great for labels hung shrubs, trees, larger perennials. Too time consuming for me, though, except for very special specimens!

I'm glad I re-read this thread, though. I use vinyl mini blind vanes for plant tags, and a neighbor gave me a bunch of old blinds that I realized too late (after they were in my basement) were aluminum rather than vinyl... I'm going to try etching or impressing on them.

Currently, I'm more likely to just grab an "extreme" black sharpie marker and a length of mini-blind, because I got really behind on labels and generally less organized the past few years. But when I can manage it, I do like to make labels by printing them with a laser printer onto clear laser address labels (they fit on most plant markers and also on mini blinds). They've lasted a good 10 years for me, at least those that didn't get displaced and lost!