Dictionaries and Thesauri

• Oxford Dictionary Online Free version includes the dictionary with limited functionality, links to writing tips, language learning puzzles and games, and some resources for English learners. Oxford also offers free access to the Advanced American Dictionary for Learners of English
• Cambridge Dictionaries includes American English, Business English, and a Learner's Dictionary
• Merriam-Webster Dictionary
• Farlex Free Dictionary includes English, Spanish, German, French, Italian, Chinese, Portuguese, Dutch, Norwegian, Greek, Arabic, Polish, Turkish, Russian, Medical, Legal, and Financial Dictionaries, Thesaurus, Acronyms and Abbreviations, Idioms,Encyclopedia, and a Literature Reference Library

General Encyclopedias

• Wikipedia
• Scholarpedia Like wikipedia, below, but entries are peer reviewed
• Encyclopedia Britannica Online
• CIA World Factbook

Fulltext Reference Collections

• www.bartleby.com includes full text reference works as well as other books
• Infoplease.com large online collection of reference information and sources