Dictionary.Com -Pretty basic
Encyclopedia.Com -Includes articles from the Columbia Encyclopedia 
Encyclopedia Britannica -Subscription service.
Info. Please Almanac -Almanac, encyclopedia and dictionary!
InfoJump -5 million electronic articles in 48 categories
Merriam-Webster -Dictionary.
Ref. Desk -Internet reference desk. 
Reference.Com -Search for organizations and groups. 
Research It -Dictionary.. and more.
Roget's Thesaurus -The standard bearer.
Wikipedia -"The free encyclopedia."
World Book -Subscription based. Generally better for children.
Word Reference -Translation!
Xrefer -