Any one know of an organization dedicated to helping native americans?

hi i have felt much for the natives of this land (like jessica beil in that nic cage movie!) i have been wondering how to contribute, as is i have seen some "reservations" that look much like 3rd world countrys. it is utterly horrifying , knowing that is going on in our country, their land, their home..... any information would be helpfull . im sure more to them then me.