Benny and I love his PetHub dog tag. Having a QR code on his collar allows me to provide more information than just his phone number. If Benny ever gets lost (although it will hopefully never happen), the person that finds him can scan the QR code and find my address, his vet's name, allergies, and any other information I choose to share on Benny's profile page.
Benny wears the small aluminum tag. I used a pin to carve his name and phone number in the back just in case the person that finds him doesn't own a smart phone. Right now, you can get up to two free aluminum tags using the promotional code MEGAMATCH. You do need to pay for shipping which is why I titled my post "almost free" but it's still a great deal. The shipping prices change based on your location. For my address, shipping for one tag was $1.95 and two tags was $2.20. For that difference, I will be getting two tags so that I have a spare.
Celebrate National Adopt a Dog Month!-- for ASPCA's #megamatch event: get a #free ID tag for your new best friend (coupon: MEGAMATCH) (limit 2/person): http://PetHub.com/aspca