As at November 2007, there are 19,600,000 online dictionaries found when I just did a google.com search.
WOW!
Pretty amazing stuff! Here are some of the best free online dictionaries, which you might find useful:
The well-known Macquarie Dictionary calls itself "the record of Australian English". First published in 1981.
This is the one I used constantly! Provides free dictionary and thesaurus look-up including an online audible pronunciation database.
This online dictionary query service searches multiple online dictionary databases and returns results instantly.
Based on the best selling Newbury House Dictionary of American English, this online dictionary contains over 40,000 entries .
This portal says it is the most comprehensive and authoritative portal for language and language-related products and services on the Web. Has more than 1,800 dictionaries for over 250 languages.
This one is fantastic; called the "Faster Finder", it claims to search 700+ online dictionaries simultaneously, and has a total word count of over 4 million.