yourDictionary.com
Comprehensive index of on-line dictionaries in more than 200 different languages. Includes an index of on-line grammars, word of the day by email, and several pages of linguistic fun.

World Language Resources
Worldwide retail distribution of foreign language dictionaries in printed and electronic form. Offering hundreds of dictionaries in many languages.

WordSniffer
Multi-lingual dictionary for English, German, French, Spanish, Italian, Japanese, Chinese, and more. Offers definitions, pronunciations, and sample sentences.