This one also does Chinese Japanese and Korean, but doesn't require a download of software. You can either copy and paste text or paste in a URL so the dictionary follows you as you surf the web.
This started as a Japanese popup translator and the creator has added on Chinese and Korean. It is a Firefox add-on. Well-loved by many language learners.
This one lets you draw the characters with your mouse, and select the correct one from a list. The dictionary also includes pronunciation. Comes highly recommended by your Chinese teachers!