This is a course offered by Peking University and Coursera. It's free to use, but you need to register (you can preview it before you register, though). There are six units, each taking roughly one... Read more.

coursera.org

Word Reference offers several good forums for discussing languages and this is the Chinese section. It's perhaps not as active as Chinese Forums and I don't follow this forum regularly, so I don't... Read more.

forum.wordreference.com

Forumosa is a major online forum where you can discuss anything regarding Taiwan, including living there, learning Chinese, finding friends, jobs or language exchange partners and much more. There'... Read more.

forumosa.com

ChineseMe is the most integrated Mandarin course, designed for motivated learners who have decided to become fluent. It is an interactive textbook that adapts itself to your interests. The course i... Read more.

chinese-me.com

This is a character-by-character beginner course in Chinese, provided free of charge at the Open Languages Project. It teaches you to read (and listen to) Chinese by explaining and introducing one ... Read more.

oplang.org

This site offers basics, self-paced lessons where you can learn basic vocabulary and grammar (usually with audio as well). There are also Skype lessons and other more interactive parts of the site ... Read more.

culturealley.com