If you’re looking for a book that discusses contemporary photography- incl. many of the photographers that I already mentioned here - your search has come to an end. Charlotte Cotton’s The Photograph as Contemporary Art, part of Thames & Hudson’s utterly excellent World of Art series, is exactly the book that anybody interested in contemporary photography needs to add to his/her collection.
PS: Having just looked through the book I realized how many of the leading contemporary photographers can already be found here. But get the book anyway!