I use Boomerang Tags they are a stainless steel tag that doesn't wear off like aluminum or nickel tags. Aluminum tags are the tags you get from pets stores, the ones that are issued for city/county pet licenses, rabies tags. All of those, ever notice how quickly that the engraving wears off? It is because the metal is soft. Stainless still will last much longer, I have used Boomerang tags for years and every time I have had to order new tags (because of moving) they last without wearing down and are still always readable.
I'm not pitching Boomerang tags, Ivoss' link uses stainless steel tags too. Another great thing about the stainless steel tags is that they won't discolor the dogs fur like the aluminum or nickel tags. Or if your dogs has a nickel allergy. I have the "required tags"-rabies & city license in a tag bag on my guys because they wear out from rubbing and then I just have their ID tag out of the bag for quick identification.
Although one pitch towards Boomerang that I like a lot is that you can do double sided on their tags