I'm currently in the throes of applying for work experience at Anifex, the company that does the Schmackos ad and heaps of cool short films. Special thanks to Will's insane ability to find obscure animation companies on the net!
On their site I found some websites that look pretty good:
Stop Motion Magazine: www.stopmotionmagazine.com 
Stop Motion Works: www.stopmotionworks.com 
Stop Motion Animation: www.stopmotionanimation.com
Animate Clay: www.animateclay.com