Books
Amazon Biggest bookseller on the web, especially useful for customer reviews http://www.amazon.com
Project Gutenberg Huge collection of free electronic books, many classics http://www.gutenberg.org/wiki/Main_Page
Fiction Online
Anotherealm Website offering links to free online novels and short stories http://free-online-novels.com
Cold Frontier Personal website with free science fiction http://www.cold-frontier.com
Free Online Novels A free monthly magazine featuring science fiction, fantasy and horror http://www.anotherealm.com
SFWA Fiction online from members of the Science Fiction and Fantasy Writers of America http://www.sfwa.org/for-readers/member-fiction-online/
General knowledge
Wikipedia Freely accessible encyclopedia, in many languages, compiled by users, quality very variable but often surprisingly good http://en.wikipedia.org/wiki/Main_Page
World Factbook Brief, up-to-date information about all the countries of the world, collected by the American CIA https://www.cia.gov/library/publications/the-world-factbook/index.html
Magazines
Analog Science Fiction Magazine http://www.analogsf.com
Azimov's Science Fiction Science Fiction Magazine http://www.asimovs.com
Locus Magazine about SF, Fantasy and Horror http://locusmag.com
Rue Morgue Magazine of horror in entertainment and covers all the media http://www.rue-morgue.com
Writers' resources
Preditors and Editors A guide to publishers and publishing services for serious writers

http://www.anotherealm.com/prededitors