I would like to recommend the book Skyscraper for the XXI Century. The book includes the most innovative designs for skyscrapers.
" eVolo presents the best 60 projects of the 2006, 2007, and 2008 Skyscraper Competition. An investigation by architects, students, and designers on the future of the skyscraper. What is the skyscraper in the beginning of the XXI Century? What is the historical and social context of these mega-structures? What is their response to the urban fabric? Is the modern skyscraper a city in and of itself? Is the human scale lost?"
available at http://www.evolo-arch.com and at amazon.com