Books

Schlumberger Oilfield Glossary - With more than 4600 entries it constitutes an instant technical reference for both the generalist and the expert oil geologist
http://www.glossary.oilfield.slb.com/

North American stratigraphic code (2005) - A reference book published under the aegis of the North American Commission on Stratigraphic Nomenclature.
http://ngmdb.usgs.gov/Info/NACSN/Code2/code2.html

Alluvial Fan Flooding (1996) - This book is edited by the Commission on Geosciences, Environment and Resources (CGER) and published by the National Academies Press. It deals with alluvial fans that are known as gently sloping, fan-shaped landforms created over time by deposition of eroded sediment, and that are common at the base of mountain ranges in arid and semiarid regions.
http://www.nap.edu/books/0309055423/html/index.html

International Stratigraphic Guide - The second edition of the International Stratigraphic Guide, edited by Amos Salvador, was prepared by the International Subcommission on Stratigraphic Classification of the International Commission on Stratigraphy and co-published in 1994 by the International Union of Geological Sciences and the Geological Society of America. Here is an abridged version of this guide.
http://www.stratigraphy.org/guide.htm

Bedform Sedimentology Studies - Information about ripples, dunes, and sedimentary structures including, explanatory text, computer-generated images and movies, photographs, and bedform-simulation software provided by the USGS.
http://walrus.wr.usgs.gov/seds/

Low–temperature formation of Dolomite and Magnesite - Latest version (2005) of the open-access e-book authored by J.C. Deelman on dolomitization and related phenomena. A total of 505 text pages, including a number of graphs, drawings and photographs.
http://www.jcdeelman.demon.nl/dolomite/bookprospectus.html

Petrology of sedimentary rocks - Although long out of print, the seminal book (a total of 182 pages in a single pdf file) by R.L. Folk (1974) remains an excellent resource if you are interested in sedimentary rocks.
http://www.lib.utexas.edu/geo/folkready/

Reports of the Illinois Geological Survey authored by A.H. Worthen - This set of 8 volumes published between 1866 and 1890 is a rich resource of information about Illinois geology, landscape and mineral resources.
http://worthen.lib.uchicago.edu/

Principles of Geology, by Charles Lyell 1830 - Electronic facsimile of one of the founding book of the geological sciences, made available by Electronic Scholarly Publishing
http://www.esp.org/books/lyell/principles/facsimile/