What are Name Tags used for?

[WaLLy]

Found 2 name tags at a zombie spawn. Anyone know what I can use them for?

 

[NickHouston]

Name animals like Horses, Dogs and Cats. Maybe even the Testificates.

Edit: Not really sure about the testificates though lol[DOUBLEPOST=1397093453][/DOUBLEPOST]Ohhh and I think you need an anvil to set the name

 

[Kreubs]

To add to what Nick said, mobs named with name tags do not naturally despawn.