You might wish to consult also other lists and collections
Particularly recommended: Project Gutenberg chemistry section.
 

Free, online CHEMISTRY BOOKS

• Basic Principles of Organic Chemistry by John D.Roberts and Marjorie C.Caserio (1977).
• Bioinorganic Chemistry by I.Bertini, H.B.Gray, S.J.Lippard, J.S.Valentine. 29 MB!
• CCPS Combined Glossary of Terms on the CCPS Publications site. 164 pages.
• Chem 1 Virtual Textbook by Stephen Lower. Excellent.
• Chemistry of Drugs and Poisons in Humans. Link to PDF (2.2 MByte).
• Chemogenesis by Mark R.Leach. Excellent.
• DOE Standards books (DOE stands for the US Department of Energy):
     DOE Fundamentals Handbook, Chemistry, Volume 1 and Volume 2
     Guide to Good Practices for Training and Qualification of Chemical Operators
     DOE Fundamentals Handbook, Material Science, Volume 1 and Volume 2
     Primer on Lead-Acid Storage Batteries
     Primer on Spontaneous Heating and Pyrophoricity (also as HTML)
• Drugs and Poisons in Humans: A Handbook of Practical Analysis,
  edited by O.Suzuki and K.Watanabe (2005). Link to PDF (15 MByte) or printed version.
• Fundamentals of Chemical Reaction Engineering
  by Mark Davis and Robert Davis (2002). Available also in print.
• Modern Methods and Algorithms of Quantum Chemistry,
  Proceedings edited by Johannes Grotendorst.
• NIST Chemistry Webbook (chemical databases).
• Notes on Molecular Orbital Calculations by John D.Roberts (1961).
• Organic Chemistry by Sally and Richard Daley. Excellent. You must register, but it is free.
  Click here for an alternative source (there are zip files under the Table of Contents).
• Organometallic HyperText Book by Rob Toreki.
• Photophysics of Conjugated Polymers and Fullerenes, edited by Niyazi Serdar Sariciftci.
• Quantum Mechanics in Chemistry by Jeff Simons and Jeff Nichols.
• Quantum Monte Carlo methods for the solution of the Schroedinger equation for molecular systems by Alán Aspuru-Guzik and William A.Lester Jr.
• The ABC of DFT by Kieron Burke and friends at UCIrvine. See also the related resources.
• The Golden Book of Chemistry Experiments by Robert Brent, with illustrations by Harry Lazarus. This great chemistry book for kids is now deemed too dangerous for them (though, as a boy, I did most of the experiments myself). There is also an alternative source.
• Toxicological Chemistry and Biochemistry
  by S.E.Manahan (2002). Link to PDF (6.2 MByte) or printed version.
• Upper Limit in Mendeleev's Periodic Table - Element No.155
  by Albert Khazan in Progress in Physics. New, updated version.
  Original publication: Svenska Fysikarkivet, Stockholm, 2010, ISBN 978-9185917105.
• Virtual Chembook by Charles E.Ophardt.

Free, online books RELATED to CHEMISTRY

• From Computational Biophysics to Systems Biology (CBSB07), NIC Volume 36,
  Edited by U.H.E.Hansmann et al. Proceedings of CBSB07.
• NIC Symposium 2006, NIC Volume 32,
  Proceedings edited by Münster et al. High-end scientific computing, including Chemistry.
• NIC Workshop: From Computational Biophysics to Systems Biology 2006, NIC Volume 34,
  Edited by U.H.E.Hansmann et al. Proceedings of CBSB06.
• High Performance Computing in Chemistry, edited by Johannes Grotendorst.
• Numerical Methods and Modeling for Chemical Engineers
  by Mark Davis (1984). Available also in print.

Free, online Courses, Lecture Notes and Textbooks about CHEMISTRY

• A Spectroscopy Companion course by Masaru Kuno (2006).
• A Brief Review of Elementary Quantum Chemistry,
  lecture notes by C. David Sherrill.
• An Introduction to Relativistic Electronic Structure Theory in Quantum Chemistry,
  lecture notes by Brian Kellogg (1996) at CCC.
• Applied Chemical Kinetics, lecture notes by Mark T.Swihart (2008).
• Chimica Generale e Inorganica, a course by Ivano Bertini. In Italiano.
• Chimie Inorganique, a course by L.Jullien. In French.
• Chimie Organique I: Structure, a course by L.Jullien. In French.
• Chimie Organique II: Réactivité, a course by L.Jullien. In French.
• Environmental Chemistry lecture notes (ENV440, Northern Arizona University).
• Introduction to Nanoscience and Nanotechnology: A Workbook by Masaru Kuno (2005).
• Introductory University Chemistry Course, Part 1 and Part 2 by Jim Plambeck. Great!
• Introduzione al laboratorio di chimica organica di Luigi Garlaschelli. In Italiano.
• Méthodes Quantiques: Élements de Chimie Quantique,
  lecture notes by Bernard Silvi. In French.
• MIT Open Courses in Chemical Engineering.
• MIT Open Courses in Chemistry.
• MIT Open Courses in Materials Science and Engineering.
• Physical Description of Chemical Systems, lecture notes by Geoffrey A.Blake.
• Quantum Chemistry online course by S.M.Blinder (University of Michigan).
• Quantum Chemistry Lecture Notes by C.David Sherrill et al (Gatech). Very good.
• Quantum Chemistry Lectures at the Center for Computational Chemistry (Uni Giorgia).
• Quantum Mechanics, a basic course for chemists by Masaru Kuno (2008).
• Quantum Mechanics and Spectroscopy, a workbook for chemists by Masaru Kuno (2004).
• Thermodynamics, lecture notes by Zoltan S.Spakovszky (MIT). Exhaustive and excellent.
• Virtual Textbook of Organic Chemistry by William Reusch. Excellent.

Free, online CHEMISTRY THESES

Do you want to have your Thesis listed here? Let me know the link or send me the PDF.