An electronic book, usually, is a book published in electronic form that can be downloaded to computers. Over the Internet, you cand find almost everything by doing the right search. Here is a list of free E-Books sites.

O'Reilly online:

http://www.oreilly.com/openbook/ | http://sysadmin.oreilly.com/ 

Computer books and manuals:

http://www.adobe.com/products/acrobat/webbuy/freebooks.html 

The Network Book:

http://www.cs.columbia.edu/netbook/

Security, privacy and cryptography

http://theory.lcs.mit.edu/~rivest/crypto-security.html

Linux documentation:

http://www.tldp.org/tldp-redirect.php?url=/docs.html

FreeBSD documentation:

http://www.freebsd.org/tutorials/

SGI documentation:

http://techpubs.sgi.com/library/tpl/cgi-bin/init.cgi

IBM Online Redbooks:

http://www.redbooks.ibm.com/

UNIX stuff

http://www.ucs.ed.ac.uk/~unixhelp/index.html | http://www.uwsg.indiana.edu/usail/ |  http://www.cs.buffalo.edu/~milun/unix.programming.html

Programmers reading:

http://www.programmersheaven.com/

Programming Pearls 2nd edition:

http://www.cs.bell-labs.com/cm/cs/pearls/

C stuff:

http://www.strath.ac.uk/CC/Courses/NewCcourse/ccourse.html |  http://www.cprogramming.com/tutorial.html

Perl stuff:

http://www.webdesigns1.com/perl/ir.html | http://www.ictp.trieste.it/texi/perl/perl_toc.html |  http://www.plover.com/~mjd/perl/

Lisp stuff:

http://www.cs.cmu.edu/afs/cs.cmu.edu/project/ai-repository/ai/html/cltl/mirrors.html

Ada stuff:

http://www.adahome.com/Tutorials/

Handbook of Applied Cryptography

http://www.cacr.math.uwaterloo.ca/hac/

X Window System

http://tronche.com/gui/x/

GTK and Gnome stuff

http://developer.gnome.org/doc/GGAD/ggad.html

QT and KDE stuff

http://www.troll.no/qt/ | http://developer.kde.org/documentation/tutorials/index.html

Misc programmers reading

http://www.ic.arizona.edu/~nromano/spring99/readings.htm

Some useful tech articles

http://www.sysadminmag.com/

IBM's History

http://www-03.ibm.com/ibm/history/

Electronic Publishing

http://www.civeng.carleton.ca/~nholtz/ElectronicPublishing.html

Digital processing

http://www.dspguide.com/pdfbook.htm

The Hardware Book

http://sunsite.auc.dk/hwb/

Cisco Product Documentation

http://www.cisco.com/univercd/cc/td/doc/product/

Books and texts

http://digital.library.upenn.edu/books/

Seven Wonders of the World

http://ce.eng.usf.edu/pharos/wonders/

Medieval history

http://www.fordham.edu/halsall/sbook2.html

The Dead Sea Scrolls

http://lcweb.loc.gov/exhibits/scrolls/toc.html

The constellations

http://www.dibonsmith.com/constel.htm

Falling into a black hole

http://casasrv.colorado.edu/~ajsh/schw.shtml