My favorite resources as follows:
#1 Curezone
#2 The Amazing Liver & Gallbladder Flush by Andreas Moritz www.ener-chi.com
#3 Healthy Liver and Bowel Book by Dr. Sandra Cabot www.liverdoctor.com
#4 Sensible Health website with Julia Chang www.sensiblehealth.com
#5 SA Wilson's coffee enema literature www.sawilsons.com/library.htm This website will give you a lot of links to other websites.
#6 The Healing Crisis by Bruce Fife (A must read if you are detoxing, it explains why you feel crappy during cleansing)
I am sure there are more but this will give you a good start. There are also lists of books on Curezone, some are free to read online. Check out the pages here about liver cleansing, enemas and detox:
www.curezone.com/cleanse/liver/
www.curezone.com/cleanse/bowel/default.asp
www.curezone.com/cleanse/enema/