China National Knowledge Infrastructure (CNKI) 中国知网 - provides the most comprehensive and current information on a world-wide scale.
WANFANG DATA 万方数据-中国数字化期刊群-- provides multi-disciplinary full-text online journals covering scientific, technical, medical and social sciences literature.

[References on Chinese Culture and Heritage]

Chinese Heritage Centre 华裔馆
Chinese Overseas Studies 新加坡国立大学图书馆藏海外华人研究
八方文化—中文书刊之窗— A window for Chinese publishing in Singapore.
哈佛燕京学社-Harvard-Yenching.net— A website about Chinese culture and history, focusing on Confucian, created and maintained by Department of EALC, Harvard University.
世界华人网 World-Chinese.com— A mega-site provides information on finance, Chinese business, movie, books, law issue, Tao, Buddha, Confucianism, Chinese medicine, Chinese wisdom and prediction, both in Chinese and English.
中国历史文化遗产保护网—the Chinese cultural heritage protection web site.
国学网站—introduces research results of Chinese studies, scholars, publishing, etc.
中国文艺网—a website about Chinese culture, fine arts, food, history and classics.
中华万年网—The content, both in Chinese and English, focuses on the 100,000 years of Chinese culture, including its rich and fascinating history, biographies, travel, art, and other stories.
历史回廊—a Chinese website about world history and culture.
中国传统文化网—a Chinese website about Chinese religion, philosophy, history, literature & arts, traditional medicine, social science and e-books.
当代中国网—a Chinese website about contemporary China politics, economics, culture, military, law, diplomacy, social problems, etc.

[Free E-books]

北极星书库-- a non-profit e-books website for free-downloading.
亦凡公益图书馆-- provides free-browse and download materials.
维基文库 Wikisource -- provides free-browse and downloadable materials.

[E-dictionaries]

爱词霸-A free e-dictionary between English and Chinese.
维基词典 Wiktionary–-A free multi-language dictionary.
维基百科 Wikipemedia--A free e-encyclopedia allowing users to copy, distribute and/or modify documents under the terms.

[Discussion lists]

全球华人网—a Chinese BBS for Chinese culture and literature.
中华历史网—a Chinese BBS for Chinese history and world history.