This site by Jun Da contains a lot of very interesting resources for anyone who wants dig deeper into frequency lists. One set of data I haven't found anywhere else is a frequency list of syllables... Read more.

lingua.mtsu.edu

This article describes the basics of way to teach tones that is different from the traditional way mainly in that the third tone is no longer described as a falling-rising tone (since that is rarel... Read more.

sinosplice.com

This is the best overview of spaced repetition research I have seen online or offline. It's thorough, well-argued and probably covers more than you were looking for. It's not specifically about Chi... Read more.

gwern.net

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

Duanmu San's "The Phonology of Standard Chinese" is by far the best introduction to Mandarin phonology that I'm aware of. It's mostly useful for people who like phonology or are already at an advan... Read more.

hackingchinese.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

This is a unique resource that shows how most common speech sounds are actually produced. Most other resources use animations and diagrams, but this is the frist I see which show actual MRI scans. ... Read more.

seeingspeech.ac.uk