other mix resources are:Puremix.net
- has some tutorials and every once in a while they do mixing competions where everyone mixes the same song and you can win some stuff in addition to learning.
Also, there's Gearslutz
and The Womb
with their MixIt event. where you can browse many past mixoffs.
One of the most valuable resources used to be the IMP
event at ProSoundWeb it used to be a regular thing and the gem was that people actually took the time to review their peers' mixes and offer advice and ask questions.