SPIE is an international society advancing an interdisciplinary approach to the science and application of light (formerly the Society of Photo-Optical Instrumentation Engineers) and they have launched their digital library. The launch includes 120 SPIE Press titles from the Field Guides, Monographs, and Tutorial Texts series. Over the course of 2010 at least 15 new titles and editions will be added to the SPIE eBooks collection, followed by print publication.
SPIE ebooks cover important topics in optics, photonics, and imaging at all levels of complexity in authoritative professional reference books, textbooks, and handbooks covering theory and state-of-the-art applications.
The ebooks do not have any DRM. More info here.
(via Resource Shelf)