Many people consider Shamanism to be only a Native American tradition
Actually, every culture on the earth has had Shamanic aspects at one time
or another.  In a Norse context, the seidhr trance is unmistakably Shamanic,
and the ordeal of Odin on the World Tree is common to many other peoples --
the World Tree itself is a universal Shamanic concept, as is the idea of
climbing such a tree to gain wisdom, and the sacrifice/death/rebirth.
        For those with a scholarly interest, I recommend Mircea Eliade's
SHAMANISM: ARCHAIC TECHNIQUES OF ECSTASY, a well-rounded and comprehensive
survey of the world's Shamanic traditions.  For those who like illustrations,
I recommend STONES, BONES, AND SKIN: RITUAL AND SHAMANIC ART, a reprint of
an issue of ArtsCanada magazine.  The Eliade is available in a paperback
edition by Princeton/Bollingen.  The ArtsCanada book is available as a
paperback reprint or a hardback with additional articles.  In the SF Bay
Area, you can get the former at Shambhala in Berkeley, and the latter at
the Nature Company (unfortunately expensive, but worth it).  Both are also
available at the Anthro library of your local University, or you should
demand to know why not.
        For those desiring a practical approach, I suggest Michael Harner's
WAY OF THE SHAMAN.  It provides a good grounding in the basics of North
American Shamanism.  Beware, by the way, of most other books by "European"
Americans on the subject; too many of them tend to an attitude of "I'm the
special White Person the Indians chose to teach their secrets to, and only
through my guru-ship can you walk this Way."  In a word: bullshit.  As for
the Castaneda books, and those by Lynn Andrews, if the reader is worried
by the rascal-Zen-guru-ness of the respective teachers, be aware that some
but not all people need that kind of mindfucking to change their attitudes.
Quite a number don't; it just depends on your state of mind to begin with.
        Good spirit-journeying!
        SeaHawk