I recently joined the bone marrow donors registry. Bone marrow donation is easy and safe. You can be someone's cure. Join us!
Daniel explains very well the whole donation process in this video (in Spanish).
If you are located in Spain, the Josep Carreras Foundation can provide you all the information you need to join the Spanish Bone Marrow Donors Registry (REDMO).
"Unidos por la medula" is a non-profit organization that can provide you detailed information about bone marrow donation.