I just get mine done at the local pet store... I think Petsmart and Petco do them too. They're aluminum, so they're lightweight, and are engraved. Some of mine have lasted for years and years. My mom's boster terrier has had his for around 5 years, and it still looks fine.
As far as what to put, mine can be engraved on the front and back. On the front, I put their name, and 2 phone numbers. On the back, I put my address and the word reward. So my guys' tags look like this:
(front)
Jake
000-000-0000
000-000-0000
(back)
0000 Road Name Ave.
City Name, LA
REWARD
I also have a tag engraved with their microchip information, as their plastic original microchip tags are attached to their harness.
The microchip tags I engrave look like this:
(front)
MICROCHIPPED
0000-0000-0000
(back)
REWARD
And on top of that (LOL), my guys who have health issues have medical alert tags engraved. The front has the medical alert symbol, and the words medical alert. The back has their conditon.
For example, the back of Jake's tag reads:
HEART PROBS
ON MEDS
REWARD
Sam's reads:
DEATHLY
ALLERGIC
ON MEDS
REWARD
And Emmy's reads:
EPILEPTIC
ON MEDS
REWARD
Yeah I rambled, sorry, LOL. Anyways, you can put whatever you feel necessary on the ID tag. It can just be a phone number, or a name, phone number and address. Up to you on how much info you want. I put all my info, because I live in a very small town, so if my dogs ever got out or loose, I want them to know that the dog lives in this town and on exactly what street. All my tags are in addition to their rabies tags. Yeah, my guys are well ID'ed.