I will be gradually adding more links as I go along.

Australian Children's and YA writers:

Paul Collins and the Quentaris books (my title 'Pirates of Quentaris' was published in May 2006)
Meredith Costain
John Marsden
Sheryl Gwyther
Gabrielle Wang

Tracey Rolfe

Overseas 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.
Hope Marston - I met Hope at Chatauqua Writers' Workshop too - check out her non-fiction. The Little Books have beautiful illustrations.

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.
SCBWI Australia

Australian Society of Authors

Australian Writers' Centres - in every state and territory.