Did early attempts at computer translation really translate "out of site, out of mind" into "blind idiot"? The Urban Legends Reference Pages have the answer.
Babylon is an on-screen translator. Download and install Babylon for free and you can have instant translation from English to one of several languages in any Windows program.
Cambridge International Dictionaries Online: search the Cambridge International Dictionary of English, Cambridge Dictionary of American English, Cambridge International Dictionary of Phrasal Verbs or Cambridge International Dictionary of Idioms.
WWWebster dictionary and Thesaurus One of the best online dictionaries I've come across. Fast, efficient and gets the best results for single words and common expressions.
A searchable database containing common acronyms and abbreviations about all subjects, with a focus on computers, technology, telecommunications, and the military.
The Grammar Lady Online Very good site for all your language questions, and more. Includes English language FAQ, language forums, and more.
The LOGOS Dictionary
A multilingual database, updated and corrected on line by a network of professional translators and Internet users. It has over 7 million entries in more than 30 languages, some of them with sound recordings. Also has a fun Multilingual Crossword puzzle.
A web of online dictionaries If my links are not enough - this website indexes on-line dictionaries, thesauri, and such like containing words and phrases.