Any good art history survey book will cover sculpture, as will any survey of modern art. In reference to 20th century sculpture, Sculpture 1900-1945 by Penelope Curtis looks like it should cover what you're interested in. On the topic of Italian sculpture, apparently there is a book on the subject by Roberta J. M. Olsen that may be of interest. Are there any other time periods or places you have a particular interest in?

Wayne Craven's Sculpture in America is the standard textbook for American sculpture, if that is a particular interest. A good scholarly work on American sculpture is Kirk Savage's Standing Soldiers, Kneeling Slaves.