I recommend this dictionary for looking up the pronunciation of words: http://dictionary.cambridge.org/.
I like the fact that it has two different accent options - one American Accent and one British. The vowels and consonants are mostly pretty authentic to an American Accent. Many other online English dictionaries are confusing in this regard.
Also, if you have studied British English in your country, it's useful to hear both versions of the same word. Just for fun, look up the words, "better," "student" and "awful."
Big differences in the two different accents!
