www.chinese-forums.com  *****
Amazing forum for students of chinese. Thousands of posts about any topics of interest to the foreign learner, from where to buy squared paper to the "WOW effect" of mentionning you speak chinese. A great ressource, good quality material everywhere on the forum. Recommended!

www.mandarintools.com  ****
Excellent website by a chinese language enthusiast who studies for a PhD in linguistics at Carnegie Mellon University. Many ressources for the student, including a Java flash card software as well as tutorials to read and write chinese on a western computer.

www.cantonese.sheik.co.uk ***
Very comprehensive website about studying Cantonese by a British enthusiast. Lively discussion forum. Good discussions of Cantonese versus Mandarin and difficulties to learn Cantonese.