Encyclopedias

http://www.wikipedia.com

http://www.factmonster.com

http://www.biography.com

Dictionaries

http://dictionary.com

http://www.itools.com

http://alphadictionary.com (many languages )

http://www.wordcentral.com

Computing Dictionaries

http://www.webopedia.com

Maps

http://atlapedia.com/online/map_index.htm