English-Mandarin Chinese dictionary
Not a full-size dictionary. Chinese is Mandarin Chinese in pinyin.
Chinese Character Genealogy
More than just a dictionary. A whole website by Rick Harbaugh.
Dictionaries Thomas Chen, Leiden Univ.
English, Radical/strokes, pinyin, Cantonese, Hakka, Internal codes, etc
This is not a Chinese dictionary, but a source for English-English dictionaries. Enter a word, and it provides links to several dictionaries which define the term. This free service is the fastest, best way to find the really tough ones.
This is a wonderful demonstration of the power of the Internet. How else would you be able to look up a word in several dictionaries without leaving your seat?