Synonymous.com

Lin Yutang's Chinese-English Dictionary of Modern Usage
Chinese University of Hong Kong’s Web edition based upon the1972 dictionary with over 40,000 entries. Indexed by radical, Pinyin, and English, and searchable by full text or head character. (Big5)
humanum.arts.cuhk.edu.hk/

Mandarin Planet Chinese-English Dictionary
This CEDICT interface, with over 34,000 entries, can be searched by traditional or simplified Chinese characters, Pinyin, or English. Audio pronunciation is available. (GB, Big5, or UTF-8)
www.mandarinplanet.com/

The Lingua Sinica Chinese-English Dictionary
Currently contains over 70,000 entries, with traditional and simplified characters, Gwoyeu Romatzyh and Pinyin romanizations, WAV format pronunciations, grammatical functions, translations, and examples. Fuzzy search input through character, ASCII Pinyin, or English. (UTF-8)
linguasinica.com/

Xiaoma Cidian - Chinese English dictionary
CEDICT and Unihan server with search by simplified Chinese character, Pinyin, English, radical, stroke, or usage frequency. (UTF-8)
hmarty.free.fr/

Mandarin Book Chinese-English Dictionary
Simple CEDICT and UNIHAN interface searchable by Pinyin, traditional character, or English, and with pronunciation sound files.
www.mandarinbook.info/

Dr. Dict: English-Chinese Medical, Biological, and Technical Dictionary
Specialized online database of scientific terminology with over 420,000 entries. (GB)
www.drdict.com/

MobileCEDICT Chinese-English Dictionary
Bilingual English or Pinyin search interface for WAP-enabled cell phones and other devices capable of handling WML pages. (Big5, GB)
ktmatu.com/

Chinese-English Online Dictionary
TigerNT’s CEDICT server searchable by character, Pinyin, or English. (GB, Big5, GIF)
www.tigernt.com/

MDBG Chinese-English Dictionary
An online dictionary interface for learners of Chinese. The CEDICT word dictionary is searchable by English, character, or Mandarin Pinyin; and the UNIHAN character dictionary by English, character, Pinyin, Cantonese, radical/stroke, etc. Menus support both simplified and traditional Chinese. (UTF-8, Big5, GB)
www.mdbg.net/

Lexiconer English Chinese Dictionary
English-Chinese and Chinese-English interfaces using the Linux Chinese/English dictionary database pyDict, written in Python/GTK. (Big5, GB)
www.lexiconer.com/