Dictionary.com --- a good online dictionary (線上英英字典)

Dictionary.com (http://dictionary.reference.com/ ) is a good website for English learning because it exhibits different activities for English learning and search enginer for meanings of words which includespronunciation in audio form and International Phonetic Alphabet (IPA) in written form.
For examples,
http://dictionary.reference.com/browse/hilarious
http://dictionary.reference.com/wordoftheday/
Just check the website and click the image of voice amplifier.
The page of translator at Dictionary.com is amazing because it can translate sentence into 50 lanuages.
for example, http://translate.reference.com/translate?query=That+girl+is+beautiful.+&src=en&dst=el&v=1.0
The sentence you want to translate in top box and the resulting sentence they have translated at the bottom box. You may want to try different language.