The following bibliography is meant to cover literature on primarily peyote/Lophophora and related Mexican/Texan cactus species, but many general works on cacti are also included. The bibliography lists books and journal articles as well as relevant online material - and download links are provided for works that are publicly available online. Currently the bibliography is very much a work in progress and will be expanded in the future; it was last updated April 25, 2013 and contains 74 entries. Please let me know if you encounter any stale links or have additional references.
For further reading, well-assorted online libraries include Biodiversity Heritage Library, Botanicus Digital Library, Cactus and Succulent Digital Library, CCI Online Library, and Living Rocks of Mexico - Online Publications