I found Robert Monroe's Ultimate Journey to be extremely interesting:
http://www.amazon.com/exec/obidos/tg/detail/-/0385472080/qid=1090896891/sr=8-1/ref=pd_ka_1/104-2104024-6427928?v=glance&s=books&n=507846
Bruce Moen's books are the best follow-up for what Monroe wrote:
http://www.amazon.com/exec/obidos/search-handle-url/index=books&field-author=Moen%2C%20Bruce/104-2104024-6427928
http://www.amazon.com/exec/obidos/tg/detail/-/0385472080/qid=1090896891/sr=8-1/ref=pd_ka_1/104-2104024-6427928?v=glance&s=books&n=507846
Bruce Moen's books are the best follow-up for what Monroe wrote:
http://www.amazon.com/exec/obidos/search-handle-url/index=books&field-author=Moen%2C%20Bruce/104-2104024-6427928