URLs listed in this category:
Cambridge Dictionaries
Offers an online dictionary and sells a variety of dictionary products.
http://dictionary.cambridge.org/
Cool Dictionary
Webster-based dictionary with pronunciation audios. Also makes use of Wiktionary and Wikipedia resources.
http://www.cooldictionary.com/
Dictionary Link
Guide to free online dictionaries and translation services. Also provides links to thesauri and encyclopedias.
http://www.dictionarylink.com/
Picture Dictionary
Different from a dictionary or from encyclopedia because the images replace the words. Where words are defined as pictures, for learning the exact names of objects.
http://www.infovisual.info/