“I like the way on the iPad the dictionaries are available from different apps but I also use the free Dictionary.com and Thesaurus app as it works offline and gives me the pronunciation of words.”  Andreas

There are advertisements supporting the free version of the app.  These disappear if you pay £2.99 for the ad free version of the Dictionary.  The iPad version also appears to work on an iPhone OS 6 as can be seen in the image and you can say the word using speech recognition.

Butterscotch.com have provided a YouTube video about the Dictionary.com app and mentions that you need to be online to use the audio pronunciation.