I don't have loads of cookbooks (did a cull recently and haven't bought any new ones lately), but there are a few that I use over and over:
1: Every Day in the Kitchen, by Allan Campion and Michelle Curtis
2: The Cook's Companion, by Stephanie Alexander
3: Baby and Toddler Meal Planner, by Annabel Karmel
4: taste.com.au.....I am constantly using this website too, I love it!
Number 1 I have used so much that the book is in tatters and I'm seriously considering buying a new one online! I constantly refer to Stephanie's book, it's great when you have an ingredient and you want ideas on what to use it for, and I just love number 3, my kids love all the things I cook from it so it's been great ever since DS was a baby.
I'd be interested to hear what cookbooks others love, so feel free to share them!