I will be gradually adding more links as I go along.
Australian Children's and YA writers:
Kristi Holl - I first met Kristi at Chatauqua Writers' Workshop and she ran some great sessions on tension techniques and mysteries for middle graders. Her website has some excellent resources.
Sites about writing for children:
SCBWI - Society of Children's Book Writers and Illustrators - an international organisation for children's writers and illustrators that provides a wealth of resources. Members can download info on publishers and magazines, as well as lots of other handy stuff.