Engines of Creation - The Coming Era of Nanotechnology 1986 by K. Eric Drexler with a foreword by Marvin Minsky. This is the first and still the classic book on nanotechnology.Slashdot Book Review: Nanosystems - by K Eric Drexler. The classic textbook reviewed by Chris Worth. 10/10.
Nanomedicine - Online book (volume 1 of 3) Robert A. Freitas Jr. on applying nanotechnology to medicine. ("published" late 1999 / early 2000)
Unbounding the Future - The Nanotechnology Revolution © 1991 by K. Eric Drexler, Chris Peterson, and Gayle Pergamit. Provides a clear, nontechnical introduction to molecular manufacturing: what it is about, what it will make possible, and what are the dangers, as well as the opportunities, that will come with the development of nanotechnology.
Foresight Nanotechnology Bookstore - Nanotechnology: Molecular Speculations on Global Abundance; Nanotechnology: Research and Perspectives; Prospects in Nanotechnology: Toward Molecular Manufacturing; The First Immortal and several others
Nanotech Book Reviews - Steve Lenhert reviews his two favorite nanotech books, Travels to the Nanoworld and Nanotechnology.