I don't know if "favorites" is really applicable... My attention is "grabbed " by many, at random ...
At present - Stream of consciousness:
"20th Century Photography - Museum Ludwig Cologne." A wide collection of wonderful photography from those well-known and those who are more obscure. A wonderful "artisic block" breaker.
"Alfred Stieglitz - A Biography" by Richard Whelan. Well written microscopic study of Stieglitz - as close to a "hero" (although certainly flawed) as anyone, in my opinion.
"Worlds in a Small Room", by Irving Penn - Work by a Master - recording disappearing cultures.
"Infrared Nude Photography" by Joseph Paduano. Beautiful applications of IR.
"The Elements of Color" by Johannes Itten. Marvelous insights into the graphic-psychological interactions in man.
Partial listing - subject to change at a moment's notice.
P.S. - And I'm wandering thorugh the poetry of Rumi.