An English Pronouncing Dictionary with Instant Sound

 www.howjsay.com

Complete website with several OUP dictionaries available online:
http://www.askoxford.com/?view=uk

Free online dictionaries from CUP

http://dictionary.cambridge.org/

Here you have Merriam-Webster Dictionary Online
http://www.merriam-webster.com/

Online English dictionary and bilingual dictionary (Spanish-English-Spanish) with phonetics, forum discussions, etc.

www.wordreference.com