Free Science, Engineering and Medical Books Online. I am not lying. The National Academies Press which was created by the National Academies to publish the reports issued by the National Academy of Sciences, the National Academy of Engineering, the Institute of Medicine, and the National Research Council, all operating under a charter granted by the Congress of the United States, has more than 2,500 free, searchable, high quality books online. Some random examples: The Genomic Revolution: Unveiling the Unity of Life Strange Matters: Undiscovered Ideas at the Frontiers of Space and Time Who Goes There?: Authentication Through the Lens of Privacy Microbial Threats to Health: Emergence, Detection, and Response [kuro5hin.org]
A useful resource to have handy BUT see this post from Terry Frazier on limitations of this.