Try this online dictionary/thesaurus with built-in word pronunciation

This useful site enables you not only to find the meanings, synonyms and antonyms for words, but to hear how the words are pronounced. Anyone learning English would appreciate the latter feature.
The site includes specialized dictionaries in the fields of computing, law, medicine, and finance. You can also look up the meanings of common acronyms (like URL) and idioms in the English language. Writers will find this site invaluable.

http://www.thefreedictionary.com/dictionary.htm

Visual Thesaurus--Synonyms and Antonyms

This dictionary and thesaurus site is a valuable tool for writers. Many professional writers and educators subscribe to the site because of its interactive, intuitive visual interface. By focusing on the relationships between words and their meanings, a writer will be better able to find the precise word for a particular context. The site features a demo which allows you try the process. Audio pronunciation of words is available on the site. Both desktop and online versions are available, and subscription is reasonably priced.

The site also contains magazine articles on topics of interest to writers and educators. One section of the magazine, aptly titled “Department of word lists”, features the jargon specific to various topics, e.g. “golf”. A sports writer covering a golf story would have all the right terms close at hand.

Check it out: http://www.visualthesaurus.com/

Here is a free , non-visual site which features audio pronunciation of words:

http://www.thefreedictionary.com/