Just recently I obtained the Numero de Identidad de Extranjero, which allows me in Spain to get a job, buy a car/house etc. Very important number if you want to live in Spain for a longer time. The number you get is valid forever, you just have to renew the certificate (every 5 years).
For European Union citizens there are 2 steps involved in obtaining it. The first one is to get an appointment. You can try calling the COMISARIA GENERAL DE EXTRANJERIA to get the appointment but in my case it was easier to go to the office at 4am and wait for the registration at 9am. The good thing was that I went there with 3 friends, so we were not that bored as you can see on the pictures. Remember to bring your passport for that meeting. The officer will schedule you for an appointment that will take place after about 8 days. You will get forms needed to be filled out and a form to pay 6.70EUR for the issuance of the number.
Fill out the forms, pay the “tasa” at any bank, bring your passport, 1 photocopy of your passport and to be on the safe side, bring 3 recent photographs of yourself (I didn’t need to give them in but…). You should obtain you N.I.E. number on the same day.