Chronic,
"Inner Paths to Outer Space" is a good read about the way we are affected neurologically and spiritually by psychedelics, DMT, mushrooms, and Ayahuasca specifically.
"Supernatural" by Graham Hancock is an interesting read that also touches quite a bit on DMT and Ayahuasca, this book speculates on many esoteric beliefs i.e. faeries, aliens, changelings etc. It ties these experiences in with altered states of conciousness, pretty far out but an interesting read.
"One River" by Wade Davis is a biography of Botanist Richard Evans Schultes adventures in the amazon. Schultes samples an assortmant of botanical snuffs and brews and basically comes across as a psychedlic Indiana Jones exploring the nether regions of the jungle in search of rare and medicinal plants. I highly recommend this book!
Enjoy!